Planet Lisp

Vsevolod DyomkinImproving Lisp UX One Form at a Time

· 9 days ago

At the recent ELS, I presented a lightning talk about RUTILS and how I see it as a way of "modernizing" CL, i.e. updating the basic language elements to be simpler, clearer and more generic. Thus improving the everyday user experience and answering the complaints of outsiders about "historical cruft" in the Lisp standard. Indeed, Lisp has a lot of unrecognizable names (like mapcar and svref) or just unnecessary long ones (multiple-value-bind or defparameter), and out-of-the-box it lacks a lot of things that many current programmers are used to: unified generic accessors, generators, literal syntax for defining hash-tables or dynamic vectors etc. This may not be a problem for the people working with the language on a regular basis (or if it is they probably have a personal solution for that already), but it impedes communication with the outside world. I'd paid extra attention to that recently as I was preparing code examples for the experimental course on algorithms, which I teach now using Lisp instead of pseudocode (actually, modulo the naming/generics issue, Lisp is a great fit for that).

Unfortunately, the lightning talk format is too short for a good presentation of this topic, so here's a more elaborate post, in which I want to show a few examples from the RUTILS library of using Lisp's built-in capabilities to introduce clear, uniform, and generic syntactic abstractions that may be used alongside the standard Lisp operators, as well as replace them in the cases when we want to get more concise and understandable code.

What's cool about this problem is that, in Lisp, besides a common way to extend the language with functions and methods (and even macros/templates, which find they way into more and more languages), there are several other approaches to the problem that allow to tackle issues that can't be covered by functions and even macros. Those include, for instance, reader macros and aliasing. Aliasing is, actually, a rather simple idea (and can be, probably, implemented in other dynamic languages): duplicating functionality of existing functions or macros with a new name. The idea for such operator came from Paul Graham's "On Lisp" and it may be implemented in the following way (see a full implementation here):


(defmacro abbr (short long &optional; lambda-list)
`(progn
(cond
((macro-function ',long)
(setf (macro-function ',short) (macro-function ',long)))
((fboundp ',long)
(setf (fdefinition ',short) (fdefinition ',long))
,(when lambda-list
`(define-setf-expander ,short ,lambda-list
(values ,@(multiple-value-bind
(dummies vals store store-form access-form)
(get-setf-expansion
(cons long (remove-if (lambda (sym)
(member sym '(&optional; &key;)))
lambda-list)))
(let ((expansion-vals (mapcar (lambda (x) `(quote ,x))
(list dummies
vals
store
store-form
access-form))))
(setf (second expansion-vals)
(cons 'list vals))
expansion-vals))))))
(t (error "Can't abbreviate ~a" ',long)))
(setf (documentation ',short 'function) (documentation ',long 'function))
',short))

As you may have noticed, it is also capable of duplicating a setf-expander for a given function if the lambda-list is provided. Using abbr we can define a lot of shorthands or alternative names, and it is heavily used in RUTILS to provide more than 50 alternative names; we'll see some of them in this post. What this example shows is the malleability of Lisp, which allows approaching its own improvement from different angles depending on the problem at hand and the tradeoffs you're willing to make.

Introducing generic element access

One of the examples of historic baggage in CL is a substantial variety of different methods to access elements of collections, hash-tables, structures, and objects with no generic function unifying them. Not to say that other languages have a totally uniform accessor mechanism. Usually, there will be two or three general-purpose ways to organize it: dot notation for object field access, something square-braketish for array and other collections access, and some generic operator like get for all the other cases. And occasionally (e.g. in Python or C++) there are hooks to plug into the built-in operators. Still, it's a much smaller number than in Lisp, and what's more important, it's sufficiently distinct and non-surprising.

In Lisp, actually, nothing prevents us from doing even better — both better than the current state and than other languages — i.e. from having a fully uniform and extensible solution. At first approximation, it's just a matter of defining a generic function that will work on different container types and utilize all the existing optimized accessor functions in its methods. This interface will be extensible for any container object. In RUTILSX (a part of RUTILS where any experiments are allowed) this function is called generic-elt:


(defgeneric generic-elt (obj key &rest; keys)
(:method :around (obj key &rest; keys)
(reduce #'generic-elt keys :initial-value (call-next-method obj key))))

One important aspect you can see in this definition is the presence of an :around method that allows to chain multiple accesses in one call and dispatch each one to an appropriate basic method via call-next-method. Thus, we may write something like (generic-elt obj 'children 0 :key) to access, for instance, an element indexed by :key in a hash-table that is the first element of a sequence that is the contents of the slot children of some object obj.

The only problem with this function is its long name. Unfortunately, most of good short element access names, like elt and nth are already taken in the Common Lisp standard, while for RUTILS I've adopted a religious principle to retain full backward compatibility and don't alter anything from the standard. This is a critical point: not redefining CL, but building on top of it and extending it!

Moreover, element access has two features: it's a very common operation and it's also not a usual function that does some computation, so ideally it should have a short but prominent look in the code. The perfect solution occurred to me at one point: introduce an alias ? for it. Lisp allows to name operations with any characters, and a question mark, in my opinion, matches very well the inner intent of this operation: query a container-like object using a certain key. With it, our previous example becomes very succinct and cool: (? obj 'children 0 :key).

Additionally to element reading, there's also element write access. This operation in Lisp, like in most other languages, has a unified entry point called setf. There's a special interface to provide specific "methods" for it based on the accessor function. Yet, what to do when an access function is polymorphic? Well, provide polymorphic setter companion. (defsetf generic-elt generic-setf). Like generic-elt, generic-setf defers work to already defined specific setters:


(defmethod generic-setf ((obj list) key &rest; keys-and-val)
(setf (nth key obj) (atomize keys-and-val)))

And it also supports key chaining, so you can write: (setf (? obj 'children 0 :key) new-value).

Having this unified access functionality is nice and cool, but some people may still linger for the familiar dot object slot access syntax. We can't blame them: habits are a basis of good UX. Unfortunately, this is contrary to the Lisp way... But Lisp is a pro-choice and future-proof language: if you want something badly, even something not in the usual ways, almost always you can, actually, find a clean and supported means of implementing it. And this case is not an exception. If you can tolerate an small addition — a @-prefix to the object reference (that's also an extra prominent indicator of something unusual going on) — when accessing its slots you can define a reader macro that will expand forms @obj.slot into our (? obj 'slot) or a standard (slot-value obj 'slot). With it, we can write something like (? tokens @dep.govr.id), which is much more succinct and, arguably, readable than (elt tokens (slot-value (slot-value dep 'govr) 'id)).

Still, one issue remains unsolved in this approach: the preferred Lisp slot-access method is not via slot-value, but with an accessor method that is exported. And one of the reasons for it is that slot-names, which are usually short and can clash, are kept private to the package where they are defined. It means that in most cases @obj.slot will not work across packages. (Unlike the OO-languages in which every class is its own namespace, in Lisp, this function is not "complected" within the OO-system, and packages are a namespacing method, while objects serve for encapsulation and inheritance.)

There are two ways to tackle this problem. As I said, Lisp is future-proof: being thoroughly dynamic and extensible, CLOS defines a method that is called when there's a problem accessing an object's slot — slot-missing. Once again, we can define an :around method that will be a little smarter (?) and try to look up slot-name not only in the current package, but also in the class' original package.


(defmethod slot-missing :around
(class instance slot-name (operation (eql 'slot-value)) &optional; new-value)
(declare (ignore new-value))
(let ((class-package (symbol-package (class-name (class-of instance)))))
(if (eql class-package (symbol-package slot-name)) ;; to avoid infinite looping
(call-next-method)
(if-it (find-symbol (string-upcase slot-name) class-package)
(slot-value instance it)
(call-next-method)))))

This is a rather radical way and comes at a cost: two additional virtual function calls (of the slot-missing method itself and an additional slot-value one). But in most of the cases it may be worth paying it for convenience's sake, especially, since you can always optimize a particular call-site by changing the code to the most direct (slot-value obj 'package::slot) variant. By the way, using slot accessor method is also costlier than just slot-value, so we are compensating here somewhat. Anyway, it's cool to have all the options on the table: beautiful slow and ugly fast method that our backward-compatibility approach allows us. As usual, you can't have a cake and eat it too...

Though, sometimes, you can. :) If you think more of this it becomes apparent that slot-value could be implemented this way from the start: look up the slot name in the class'es original package. As classes or structs are defined together with their slots it is very rare if not almost impossible to see slot-names not available in the package where their class is defined (you have to explicitly use a private name from another package when defining a class to do such a trick). So, slot-value should always look for slot names in the class'es package first. We can define a "smart" slot-value variant that will do just that, and with our nice generic-elt frontend it can easily integrated without breaking backward-compatibility.


(defun smart-slot-value (object slot-name)
(slot-value object
(or (find-symbol (string-upcase slot-name)
(symbol-package (class-name (class-of instance))))
slot-name)))

Unifying variable binding with with

Almost everything in functional variable definition and binding was pioneered by Lisp at some point, including the concept of destructuring. Yet, the CL standard, once again, lacks unification in this area. There are at least 4 major constructs: let and let*, destructuring-bind and multiple-value-bind, and also a few specialized ones like with-slots or ppcre:register-groups-bind. One more thing to mention is that parallel assignment behavior of plain let can be implemented with destructuring-bind and multiple-value-bind. Overall, it just screams for uniting in a single construct, and already there have been a few attempts to do that (like metabang-bind). In RUTILS, I present a novel implementation of generic bind that has two distinct features: a more plausible name — with — and a simple method-based extension mechanism. The implementation is very simple: the binding construct selection is performed at compile-time based on the structure of the clause and, optionally, presence of special symbols in it:


(defmacro with ((&rest; bindings) &body; body)
(let ((rez body))
(dolist (binding (reverse bindings))
(:= rez `((,@(call #'expand-binding binding rez)))))
(first rez)))

A very short number of methods covering the basic cases are defined:

  • the first one expands to let or multiple-value-bind depending on the number of symbols in the clause (i.e. for multiple values you should have more than 2)
  • the second group triggers when the first element of the clause is a list and defaults to destructruing-bind, but has special behaviors for 2 symbols ? and @ generating clauses for our generic element access and smart slot access discussed in the previous section

(defun expand-binding (binding form)
(append (apply #'bind-dispatch binding)
form))

(defgeneric bind-dispatch (arg1 arg2 &rest; args)
(:method ((arg1 symbol) arg2 &rest; args)
(if args
`(multiple-value-bind (,arg1 ,arg2 ,@(butlast args)) ,(last1 args))
`(let ((,arg1 ,arg2)))))
(:method ((arg1 list) (arg2 (eql '?)) &rest; args)
`(let (,@(mapcar (lambda (var-key)
`(,(first (mklist var-key))
(? ,(first args) ,(last1 (mklist var-key)))))
arg1))))
(:method ((arg1 list) (arg2 (eql '@)) &rest; args)
(with-gensyms (obj)
`(let* ((,obj ,(first args))
,@(mapcar (lambda (var-slot)
`(,(first (mklist var-slot))
(smart-slot-value ,obj ',(last1 (mklist var-slot)))))
arg1)))))
(:method ((arg1 list) arg2 &rest; args)
`(destructuring-bind ,arg1 ,arg2)))
In a sense, it's a classic example of combining generic-functions and macros to create a clean and extensible UI. Another great benefit of using with is reduced code nesting that can become quite deep with the standard operators. Here's one of the examples from my codebase:

(with (((stack buffer ctx) @ parser)
(fs (extract-fs parser interm))
(((toks :tokens) (cache :cache)) ? ctx))
...)
And here's how it would have looked in plain CL:

(with-slots (stack buffer ctx) parser
(let ((fs (extract-fs parser interm)))
(toks (gethash :tokens ctx))
(cache (gethash :cache ctx)))
...))

Implementing simple generators on top of signals

One of my friends and a Lisp enthusiast, Valery Zamarayev, who's also a long-time Python user, once complained that the only thing that he misses in CL from Python is generators. This feature is popular in many dynamic languages, such as Ruby or Perl, and even Java 8 has introduced something similar. Sure, there are multiple ways to implement lazy evaluation in Lisp with many libraries for that, like SERIES, pygen or CLAZY. We don't have to wait for another version of the spec (especially, since it's not coming 8-)

In RUTILS I have discovered, I believe, a novel and a very clean way to implement generators — on top of the signal system. The signal or condition facility is, by the way, one of the most underappreciated assets of Common Lisp that often comes to rescue in seemingly dead ends of control flow implementation. And Kent Pitman's description of it is one of my favorite reads in Computer Science. Anyway, here's all you need to implement Python-style generators in Lisp:


(define-condition generated ()
((item :initarg :item :reader generated-item)))

(defun yield (item)
(restart-case (signal 'generated :item item)
(resume () item)))

(defmacro doing ((item generator-form &optional; result) &body; body)
(with-gensyms (e)
`(block nil
(handler-bind ((generated (lambda (,e)
(let ((,item (generated-item ,e)))
,@body
(invoke-restart (find-restart 'resume))))))
,generator-form)
,result)))

The doing macro works just like dolist, but iterating the generator form instead of an existing sequence. As you can see from this example, restarts are like generators in disguise. Or, to be more correct, they are a more general way to handle such functionality, and it takes just a thin layer of syntactic sugar to adapt them to a particular usage style.

And a few mischiefs

We have seen three different approaches to extending CL in order to accommodate new popular syntactic constructs and approaches. Lastly, I wanted to tread a little in the "danger zone" that may be considered unconventional or plain bad-style by many lispers — modifying syntax at the reader level. One thing that Clojure (following other dynamic languages before it), I believe, has proven is the importance of shorthand literal notation for popular operations. CL standard has predated this understanding: although it has specific print representations for various important objects, and even a special syntax for static arrays. Yet, the language is really future-proof in this respect, because it provides a way to hook into the reader mechanism by modifying the readtables. It was further smoothed and packaged by the popular NAMED-READTABLES library, which allows to treat readtables similar to packages. In RUTILS I have defined several extended readtables that implement a few shortcuts that are used literally in every second function or macro I define in my code. These include:

  • a shorthand notation for zero-, one- or two-argument lambda functions: ^(+ % %%) expands into (lambda (% %%) (+ % %%))
  • a literal syntax for hash-tables: #h(equal "key" "val") will create a EQUAL-hash-table with one key-value pair
  • a syntax for heredoc-strings: #/this quote (") shouldn't be escaped/# (which, unfortunately, doesn't always work smoothly in the repl)

Overall, I have experimented a lot with naming — it was sort of my obsession in this work to find short and obvious names for new things, many of which substitute the existing functionality, under the constraints of not altering what's already in the standard. For this sake, I've ventured into non-character symbols and even the keyword package — a major offence, I reckon... And here are a few of the findings I wanted to share (besides ? and with mentioned previously):

  • call is a new alias for funcall — I suppose, in the 70's it was a really fun experience to call a function hence the name, but now its too clumsy
  • get#, set#, and getset# are aliases and new operations for #-tables (when you can't or won't use ? for that)
  • finally, the grandest mischief is := (alongside :+, :-, :*, :/), which is an alias for setf (and, you've guessed it, incf etc). The justification for this is that everyone is confused about the -f, that setting a variable is a very important operation that we should immediately notice in our clean and functional code ;), and that := is a very familiar syntax for it even used by some languages, such as Pascal or golang. It may be controversial, but it's super-convenient.

The only thing I failed to find a proper renaming for so far is mapcar. It is another one of those emblematic operations that should be familiar to everyone, yet -car creates confusion. For now, I resist the temptation to rename map into map-into and make map smarter by using the first sequence's type for the result expression. However, there's no plausible alternative variant I was able to find even among the zoo of other language's naming of this concept. Any thoughts?

PS. Those were a few prominent examples, but RUTILS, in fact, has much more to offer. A lot of stuff was borrowed from other utility projects, as well as implemented from scratch: anaphoric operators, the famous iter — a replacement for loop, Clojure-style threading macros, a new semantic pair data type to replace cons-cells, lots of utilities to work with the standard data structures (sequences, vectors, hash-tables, strings) making them truly first-class, iteration with explicit indices etc etc. With all that in the toolbox, there's now no ground to claim that Lisp is in any aspect inferior in terms of day-to-day UX compared to some other language, be it Haskell, Ruby or Clojure. Surely, I'm not talking about the semantic differences here.

Wimpie NortjeDo you really want to use conditional compilation?

· 10 days ago

Edit (2016-05-18): Use featurep to improve readability in run time check. Thanks to @ogamita for the pointer.

Edit (2016-05-21): Fix spelling mistakes. featurep not featuresp. Thanks to @ngnghm for pointing that out.

How do I conditionally include code?

When code must change behaviour based on build time settings people often reach for the conditional reader macros (#+ and #-).

These macros have two properties one must be aware of.

  1. The compiler sees different code based on the condition.
  2. The macros are only evaluated at compile time.

Another thing to be aware of is that ASDF only recompiles files when their modification timestamps have changed. This is an optimization to decrease compilation time.

There are two situations where conditional code inclusion are most often used. The first is for writing code which is portable between different computing environments and the second is for setting behaviour options at build time.

In the first scenario the same source file must work on different platforms (e.g. 32 bit and 64 bit) and different compilers. The variance in target environments makes it a necessity to present different code to the compiler based on the environment. Once the file is compiled there is no reason to recompile it until it is moved to a new environment. For this scenario the two properties above (and ASDF's partial compilation) is exactly what is needed and the correct solution is the #+ and #- macros.

The second scenario happens when the application's behaviour can be modified by setting appropriate variables at build time. This technique if often used to switch a code base between development and production modes.

If conditional macros are used to perform this task it is easy to end up with files which were compiled under different conditions. This will almost certainly result in transient bugs, i.e. bugs which disappear when the complete project is recompiled.

Since a complete recompile avoids transient bugs the next logical step is to do a complete recompile every time strange behaviour is encountered. Doing such a recompile negates much of the benefit of ASDF's partial compilation.

Another issue is that compiling different code based on the environment means that you can never test the complete code base in a single environment. One problem with this is that there is always uncertainty about the source of a bug which is present in only one of the environments. Another problem is that one can get into a situation where buggy code is only ever present in an environment with no debugging facilities1.

In summary, using conditional macros to implement build time settings have the following problems2:

  • Transient bugs,
  • Long compile times, and
  • Multiple execution environments.

These problems can be avoided while keeping the build time settings by using run time checks instead of compile time checks. The code examples below illustrate both the compile time and run time methods.

Conditional behaviour using reader macros

This method causes trouble.

(pushnew :app-release *FEATURES*)

#+app-release
(do-release-stuff)
#-app-release
(do-dev-stuff)

Conditional behaviour using run time checks

One possible solution to rid your code of conditional macros.

(pushnew :app-release *FEATURES*)

(if (uiop:featurep :app-release) 
    (do-release-stuff)
    (do-dev-stuff))

Conditional reader macros or run time detection?

Though I have not seen much discussion about this topic, I have seen a few projects which implement build time settings as I suggest in this post.

Method Use case
#+ and #- The same functionality is implemented by different pieces of code for different environments.
Run time detection. Different behaviours are selected based on build time options.

  1. An example is to move between SLIME and Buildapp with debugging disabled.

  2. Also see Buildapp fails when using uncompiled libraries for another problem caused by conditional macros.

Nicolas Hafner9th European Lisp Symposium - Confession 62

· 15 days ago

header
As I'm writing this I'm still in Krakow. Sitting next to me is Till, who joined me for ELS this year. It was a blast, but I'm also really exhausted and my throat is still hurting a bit from talking all the time the past three days. Our flight back to Zürich is in about an hour from now and I have a test to study for on the coming Thursday; I actually would've really liked to stay a bit longer, especially considering there were a few people I would've loved to talk to a bit more. Alas, you can't always get what you want.

But before I go through the entire thing by backtracking, let's instead reverse time all the way back to Sunday. Our flight to Krakow was scheduled for 17:00, so we had ample time to lounge around at home and try to relax a bit before the inevitable stress that is airport security and flying in general. Till had also packed way too much stuff, so we unloaded a bunch to make the carrying lighter. In hindsight I'm really glad we did that, as it turned out that we had to walk around quite a bit in Krakow.

At around two we then set off for the airport, where we had a quick lunch and noticed that Till had left his boarding pass in a book he had packed but we then left at home. Fortunately enough -after a bit of trouble with the Swiss website- we managed to download a copy of it to his tablet, so that all turned out fine. I suppose you really can't go for any kind of journey without at least some kind of oversight that gives you a hefty scare.

The plane we flew in was a small jet, but it was still pretty packed. I assume it was mostly Polish people returning home after a quick holiday break. On the flight my stomach got upset a bit, but otherwise it went by just fine. Once we finally arrived in Krakow we got a bit confused about the airport layout, as it was under pretty heavy construction. After some wandering about we managed to find the proper bus stop and get our tickets. I also exchanged way too much money for zloty, most of which is still in my wallet now. I didn't get much of an opportunity to waste it.

The bus ride to the hotel took around three quarters of an hour, so we got to have a good look around the outskirts of the city and its landscapes. The hotel itself was located in an area that looked rather worn down, the streets were not up to par and long stretches of the sidewalk were opened up for construction. After check-in and a short look-see at our room we decided to head on down to the bar and wait for someone to show up. Most of the conference people had already arrived in Krakow before us and were having a jolly time at the pre-conference registration party from what I overheard.

About an hour later we were joined by Christian Schafmeister and Joram Schrijver and the discussions immediately fired up. We talked a lot about Clasp and its near future- Christian was pretty worried about what he could show for his talk. He had the impression that people wouldn't be impressed by a new Common Lisp alone. I can't say I agree with that viewpoint, Clasp brings a lot of new stuff to the table that makes it a great addition to the list of implementations. The C++ interop alone is already noteworthy enough, but there's lots of smaller features that could prove very useful for larger projects. The biggest problem with Clasp remains however; there's just not enough people working on it to move it along quicker. Even with Christian's incredible speed and dedication, there's only so much he can do on his own. I've been trying to push Clasp into a situation where it is more accessible to other people for quite a while now, but especially with recent changes there's a lot left to be done for that- something that was reflected again throughout the discussions we had during the conference.

Later we were joined by a group of other lispers that were just returning from their previous party to start a new one at the bar. Things got rather lively and all sorts of topics got brought up. At around midnight I had to excuse myself however, as I wanted to be at least somewhat fresh on the coming morning. The hotel room was alright, at least it didn't smell terribly and was otherwise nicely roomy. Unfortunately the heating was also turned up enough that I couldn't fall asleep for about an hour. Opening the window cooled things down sufficiently and we finally managed to get some good rest in.

Finding the conference building in the morning was a bit tricky, but we managed to discover a kiosk along the way to get some snacks and drinks in. The conference provided for plenty of that on its own, but I was still glad to have a nice bottle of ice tea in my bag at all times. We got to the conference hall on time for the registration, but the actual conference organisation was oddly delayed. Nevertheless, discussion between the few people that had already showed up sparked almost immediately, so it didn't feel like we had to wait at all.

It was great to see Robert Strandh again as well, although I barely got to talk to him this year, much to my dismay. I'm hoping to remedy that next year. I also met Masatoshi Sano again, but I only got to talk to him on the second day. I met a few other people that I already knew from the previous ELS and had the pleasure of talking to them, but I unfortunately am terrible at remembering names, so I can't list them all here. My apologies.

Moving on to the talks. The first was about Lexical Closures and Complexity, by Francis Sergeraert. At points it was unfortunately -despite the rather heavy focus on Math at ETH- a bit over my head or moving too quickly, so I had a bit of trouble following along what exactly was happening. From what I could gather he uses closures to model potentially infinite or very large problem spaces and then perform various computations and mappings on those, thus still being able to compute real-value results without wasting enormous amounts of resources to try and model it all.

Next up was the language design section of the talks, the first of which focused on automated refactoring tools to aid students in finding style problems in their Racket code. It was fairly interesting to see a brief introduction to the tools used to both analyse and restructure source forms automatically to determine more succinct and idiomatic ways of achieving the same semantic result. It was also rather depressing to see some real-world snippets of code they had gathered from actual students. I can't say I'm surprised that this kind of absolutely horrendous code gets written by people being introduced to a language or programming in general, but one can't help but wonder if these 20-level nested ifs might stem from something other than the writer being new to it.

Following this was the demonstration of a library that extended the CL type system for a way to type-check sequences, allowing you to express things like plists as a type that you otherwise could not. It appears to me that this system might prove useful for succinct pattern checking, but unfortunately because these type definitions don't actually really communicate with the compiler in any way it is rather useless for inference or other potential optimisations that could be done if the compiler had actual knowledge of what kind of structure is being described. The code presented also used (declare (type ..)), which is the wrong way to go about something like this. Declarations are intended as promises from the programmer to the compiler. That all sane compilers also insert checks for the type on standard optimisation levels is not something that should be relied upon. check-type on the other hand would be perfectly suitable for this. However, at that point you might as well drop the type charade altogether and just have something like a check-pattern function that performs the test. Still, the talk presented an interesting view into how the actual sequence type descriptors are compiled into efficient finite state machines. The mechanism behind the type set merging was very intriguing.

Afterwards we heard a talk from Robert about his implementation of editor buffers, presenting an efficient and extensible way to handle text editing. I had read his paper on it before so I was already familiar with the ideas behind it, but it was a nice refresher to hear about it again. I'll make sure to see about hooking in his system when I inevitably get to the point of writing a source editor for QUI. It was also pretty surprising to hear about a topic like this since usually when using editors, one doesn't think about the potential efficiency problems presented by them- it all just works so well most of the time already. The biggest grievance for me in Emacs at the moment isn't necessarily the editing of text itself, even if that slows down to a crawl sometimes when I'm cruising about with a couple hundred cursors at the same time, no, the problem is with dynamic line wrapping. Emacs goes down to a complete crawl if you have any kind of buffer with long lines without line breaks. This however I assume has more to do with the displaying of the buffer than the internal textual manipulation algorithm. Maybe Robert has ideas for a good way to solve that problem as well.

During Lunch I had the great pleasure of meeting and talking to Chris Bagley of CEPL fame. I'll really have to look into that myself to see which parts of it can be incorporated into Trial. I'll definitely incorporate the Varjo part so that we can use sexprs for GLSL code, but there might be lots of other little gems in there that can be repurposed.

Following Lunch was the session on DSLs, starting off with a system to describe statistical tests in lisp. For this talk too I felt like I wasn't familiar enough with the areas it touched upon to really be able to appreciate what was being done. Apparently the system was used to do some hefty number-crunching. Besides, it's always great to see new discoveries in language evolution that allow a convenient description of a problem without sacrificing computational power for it.

The following talk stepped right into that line as well, presenting a high-performance image processing language called CMera (I believe). It does some really nifty stuff like automatically unrolling loops to avoid having to do edge testing in your tight loops all the time, expanding a single loop over an image into nine different parts that are all optimised for their individual parts. When comparing the code written against an implementation of the same algorithm in hand-written C++, the difference is absolutely astounding. Not only does this reduction in code size make things much more readable and maintainable, it also allows them to move much faster and prototype things quickly, all without having to sacrifice any computation speed. If anything they can gain speed by letting the compiler use higher-level information about the code to transform it into specialised and large but performant code.

Finally the last session of the day focused on demonstrations, firing right off with CL-MPI, a library to use the MPI system from within lisp while taking care of all the usual C idiosyncrasies, thus presenting a very handy API to run highly parallel and distributed code. Really interesting to me was their system to synchronise memory between the individual machines automatically. While the system seems pretty neat I couldn't help but wonder whether this might a bit too easily lead to either assuming synchronisation when none is present, or introducing a bottleneck in the system when it has to synchronise too often. Either way, I'm glad I don't have worry about highly distributed systems myself- measly threading alone is enough of a headache for me.

After this we had a really nice showing of an interactive computer vision system in Racket using the Kinect. That sounded like a very fun way to introduce students to Racket and computer vision in general. The few demos he showed also seemed very promising. Given last year's talk on computer vision, I might really have to take the time to look into this stuff more closely some time.

The last talk for the day focused on the problem of lexical variables in CL when debugging. Since lexical variables are often compiled away completely, it's tough to see their values during debugging. SBCL often does a pretty good job at retaining this information when compiling with (debug 3) in my experience, but there's certainly times when it doesn't, and I can see the value in implementing a system that can ensure that this gets preserved in every case, especially one that's portable across implementations. Apparently there's some really nasty code walking necessary to get the job done, and there's apparently still no code walker around that actually works as expected on all major implementations, which is a bit of a downer.

As usual closing off the day was a session of lightning talks. This year mine was a form of continuation on my last year's talk about Qtools. I talked very briefly about Qtools-UI, the effort to replace Qt parts that aren't extensible enough and thus provide a more convenient base for people to work with. I'm not sure if I managed to convince anyone to contribute to it, but hopefully it'll at least linger around in some people's heads so that they might remember it if they ever come across the need to write a GUI.

The rest of the lightning talks I'm afraid to say I can't quite remember. My memory is rather shoddy at the moment and the only reason I remember all the other talks is because I looked up their titles on the website. So, my apologies for skipping out on this, but I think the article is already plenty long as it is so going into detail on all these would only make it all the longer.

The first day was concluded by a Chris, Christian, Joram, Till, and I going back to the hotel for a brief chat at the bar, followed by a quest in search for pizza. We looked up a bunch of places near the hotel and went on our way. The first we encountered was too full and the other was near a campus that was filled with students drinking booze and doing BBQ; we deemed it a bit too lively for us. The third one was inside a student dorm building, but had enough space for us to spend some hours talking and eating. The pizza tasted very differently from what I'm used to. It wasn't bad, but also not really my kind of thing.

Some more talking and a good night's rest later it was already Tuesday. Time flies when you're having a blast. We got up a tad later this time around and walked through a convenience store. I was relieved to see that just like all the stores I'm used to the layout is as confusing as possible so that you have to waste lots of time walking by everything except what you're looking for.

Since we were close on time and there was a group photo to shoot we didn't get any time to talk before the first talk. It started off with a presentation of the Julia language by Stefan Karpinski. Julia seems like a really nice replacement for Matlab and I'd very much welcome it if it got more ground that way. However, some of the points that were presented here didn't really seem to make much sense to me. One thing that was emphasised as distinguishing Julia is that number types and arithmetic aren't in the specification, but rather defined in Julia code itself. This sounds like a neat little thing to do for curiosity's sake, but I just can't see the benefit of it. Not to mention that now instead of reading some pages of a spec you have to read some pages of code with possibly arcane interconnections and optimisations going on. Whether this makes anything more clear is really dubious to me. I'm guessing that this part was mostly mentioned at all to at least bring something new to the table since it would otherwise be pretty hard to impress lispers. Another thing I was confused about is that he seemed to hint at the possibility of writing functions that get the information about the inferred type of the compiler and can use that to generate different code, which is something that I've missed in CL in places where macro functions could be further optimised with that kind of information, but the example he showed didn't seem to use that in any way or even get it at all, so I'm not sure if I didn't catch that part or what exactly is going on with that.

A quick break later we got to the implementations part of the talks. Robert presented his modern implementation of the loop macro, which uses a system of combinatory parsing and full CLOS to allow it to be extensible. I'd love to have a portable way to extend loop as iterate really doesn't appeal to me much at all and there's currently nothing else that is extensible for custom sequences and clauses and the like. I'm not sure if his implementation will be adopted, but I would definitely welcome it.

The next two talks, which were about source translation in Racket and STM in Clojure, I'm sad to say I can't really talk about because I was distracted by a bug I had discovered momentarily and couldn't help myself but try to fix. I got absorbed all too easily, so I didn't catch much of it.

During the lunch break I got to talk to Masatoshi Sano for a good while, we mostly discussed the prospect of using Roswell for my Portacle project and talked about some of the difficulties or ways to deal with what I'll just call "The Windows Situation". I later talked to Joram a bit about potentially getting him involved in the Colleen3 or Trial projects, for which I'd heartily welcome some contributors or even just discussion partners. I'm very excited about the prospect of working with him on that.

And then came the big one. Christian's talk was, just like last year, pretty comparable to a bomb dropping. Some suspect that he's not of this world. Ignoring the question of his conception, hearing him in his element talking about Chemistry is always a treat. He showed off a nice demo of what CANDO is capable of and it really looks like a nicely lispy way of performing chemistry modelling. This is said from what I can tell with my practically nonexistent knowledge of chemistry, so I can't really claim to have a grasp on what you can actually do with it. Given that he's been at this for such a long time though, I'm convinced he knows what he needs to do in order to create things like what he presented to us- a perfect water filtering membrane. I'm still glad to have gotten involved with Clasp, it has given me lots of really great talking and thinking opportunities. It's exciting to listen with or discuss the in-depth details of what's going on inside Clasp. Now though Christian needs to get his chemistry stuff off the ground so that he can get enough funding to continue Clasp. Unfortunately grants have been hard to come by for him and that's a looming pressure that has been haunting the project many times before. Hopefully he'll be able to prove the worth of Clasp and Cando in the near future. I wish him all the luck.

Next up we had a presentation about the question of how different implementations of a depth of field effect perform on different hardware. This was mostly a concerning example as to how much code still needs to be tuned to the hardware it's being run on today. Maybe the effect is actually even more so now, since lots of hardware that lies in the same category is still very differing on what it is adept at. Thankfully I am mostly staying clear of such optimisation lunacy.

Some more coffee passed by and we were ready for the last session of talks for the conference. The debut was made by James Anderson, presenting his research into how source files are connected with each other and what kind of dependencies exist between them. He wrote a system that analysed the entire Quicklisp ecosystem's files for symbol references between things and then crunched all that data down into interesting graphs using his own database technology. The graphs for larger systems like qtools-ui look like a complete jumble as expected. He also mentioned the difficulties of trying to extract this kind of relationship information since he could only inspect code by reading it in. This is particularly a problem for methods, since they are likely to be defined from lots of different source files and potentially packages, but without at least type inference or even runtime information you can't really know where the dependency goes. Initially his idea for doing this seemed to be that he doesn't want to have to write the dependency information into his system definition files and the system should be able to infer it automatically. I'm not so sure that this is is a good idea, or that it is in fact such a problem. It seems like a rather minor inconvenience to me, but then again I've never written systems on a very large scale.

Closing it all off we had a presentation of Bazel and how it can be used to build Lisp. The most promising feature of it all being that you are able to use it to statically link libraries into an SBCL binary. I'm not convinced that Bazel is the tool to use for building unless you have a gigantic project or ecosystem surrounding it already however. It seems ridiculously heavy-weight and paying the price for it and its different way of configuration and operation does not seem worth the benefits unless you really need static linking and cannot do with shared libraries. Still, it gave me some things to think about for the eventual effort of writing my own build system, whenever that will happen.

Then as before we had some more lightning talks to round it all off. I didn't do a second one this time around, mostly because I didn't really know what to talk about for Trial. It did not seem finished enough to present yet. Maybe next year.

Finally the conference was rounded off by some goodbye messages from the conference organisation and the announcement that the next ELS might be happening in Brussels. We then had two hours left before the banquet. Michal Herda guided us into the inner parts of the city where we got to see some nice architecture. Along the way Chris Bagley and I chatted about the problems in writing game engines and games in general and some other assorted topics.

Once we arrived at the banquet I was pretty beat. The place we stood at looked oddly high-brow. The tables were set with all the usual you get in fancy restaurants- multiple wine glasses, forks and knives. It seemed in an odd conflict with the rest of the getup of the conference attendees. We all looked far too casual for this kind of thing. Due to my pickiness I couldn't eat much of the food that was being served either. It certainly looked fancy, but I don't think the taste was in accordance to that. From what I've heard from others or noticed in their expressions it was nothing exceptional. No matter for me either way though, since I came all this way not to eat, but to finally be with people that understood me and vice versa. And I got ample opportunity to do exactly that. During the dinner I mostly talked with Joram about Colleen3 and Markless.

Soon enough it hit 22:00 and we had to leave. Due to the long way back to the hotel and other delays in saying goodbye to everyone, we only arrived around two hours later, at which point I just slammed myself into bed after making sure that I got the boarding pass for next morning.

And so today I woke up at six, just to make sure that we had plenty of time for potential mistakes. Three quarters of an hour later we were on the bus to the airport. Half an hour later we had already passed through security and were waiting at the gate, at which point I started writing this. The flight after was rather annoying. It was pretty packed and there were lots of screaming children on board, the bane of any flight passenger. I have no idea why there were so many families on board, let alone on a Wednesday morning, let alone from Krakow to Zürich. Despite hellish screams of tortured souls haunting us along the way we made it back safely.

Now it's already 16:00 and aside from getting home and continuing to write this I only got the time to cook some nice lunch- the kitchen remains to be cleaned.

I suppose I should try to form some sort of a conclusion here to end this overly long article on a good note. If it wasn't already apparent from my descriptions, I had a grand time at the conference and I'm really glad that I could attend again this year. A huge thanks to everyone that was willing to talk to me and especially to all the people that got involved to make it all happen. Hopefully it'll happen again next year; I'm definitely looking forward to it.

For now though I have to get back to work hacking lisp. There's so much left to be done.

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Vsevolod DyomkinEuropean Lisp Symposium 2016

· 16 days ago

The last two days, I'm at the ELS2016. So far, it's being a great experience - I've actually forgotten the joy of being in one room with several dozens of Lisp enthusiasts. The peculiarity of this particular event is that it's somewhere in the middle between a scientific conference, like ACL, that I had a chance to attend in the recent years thanks to my work at Grammarly, and a tech gathering: it employs the same peer reviewed approach and a scientific presentation style you will find at the research conferences, but most of the topics are very applied and engineering-related.

Anyway, the program was really entertaining with several deep and insightful presentations (here are the proceedings). The highlights for me were the talks on the heterogenous sequences type-checker implementation based on the Lisp declare facility (that I'm growing more and more fond) by Jim Newton and a presentation of an image-processing DSL that's an excellent example of the Lisp state-of-the-art approach in DSL design by Kai Selgrad. Other things like a description of the editor buffers protocol, local variables preservation technic were also quite insightful. And other good stuff is coming...

It's also great to hear new people bringing fresh ideas alongside old-timers sharing their wisdom and perspective - one of the things I appreciate in the Common Lisp community.

Near the end, I'm going to present a lightning talk about RUTILS and how I view it as a vehicle for evolving the Common Lisp user experience.

Sugaring Lisp for the 21st Century from Vsevolod Dyomkin

Christophe Rhodesnot going to els2016

· 19 days ago

I'm not going to the European Lisp Symposium this year.

It's a shame, because this is the first one I've missed; even in the height of the confusion of having two jobs, I managed to make it to Hamburg and Zadar. But organizing ELS2015 took a lot out of me, and it feels like it's been relentless ever since; while it would be lovely to spend two days in Krakow to recharge my batteries and just listen to the good stuff that is going on, I can't quite spare the time or manage the complexity.

Some of the recent complexity: following one of those "two jobs" link might give a slightly surprising result. Yes, Teclo Networks AG was acquired by Sandvine, Inc. This involved some fairly intricate and delicate negotiations, sucking up time and energy; some minor residual issues aside, I think things are done and dusted, and it's as positive an outcome for all as could be expected.

There have also been a number of sadder outcomes recently; others have written about David MacKay's recent death; I had the privilege to be in his lecture course while he was writing Information Theory, Inference, and Learning Algorithms, and I can trace the influence of both the course material and the lecturing style on my thought and practice. I (along with many others) admire his book about energy and humanity; it is beautifully clear, and starts from the facts and argues from those. "Please don't get me wrong: I'm not trying to be pro-nuclear. I'm just pro-arithmetic." - a rallying cry for advocates of rationality. I will also remember David cheefully agreeing to play the viola for the Jesus College Music Society when some preposterous number of independent viola parts were needed (my fallible memory says "Brandenburg 3"). David's last interview is available to view; iPlayer-enabled listeners can hear Alan Blackwell's (computer scientist and double-bassist) tribute on BBC Radio 4's Last Word.

So with regret, I'm not travelling to Krakow this year; I will do my best to make the 10th European Lisp Symposium (how could I miss a nice round-numbered edition?), and in the meantime I'll raise a glass of Croatian Maraschino, courtesy of my time in Zadar, to the success of ELS 2016.

drmeisterLinking LLVM bitcode files for a dynamic language

· 22 days ago

Clasp Common Lisp is a dynamic language in which every top-level form needs to be evaluated in the top level environment. Clasp compiles Common Lisp code to bitcode files and then links them together into a shared library or an executable. When the library or the executable are loaded, each top-level form needs to be evaluated. This is until Clasp gains the ability to save a running environment to a file, which it doesn’t have yet. Even then, the ability to play back the top-level forms will be needed to create the environment to write to a file.

So the compiled bitcode files need to keep track of the top-level forms so that they can be played back at startup. Clasp does this by defining a “main” function with internal linkage (called “run-all”) for each llvm::Module. “run-all” evaluates every top-level form that was compiled into the llvm:Module. The tricky part is how does this main function get exposed to the outside world so that it can be called if a single bitcode file is loaded into clasp or linked together into a library or executable and invoked with other “run-all” functions from other modules.

Clasp creates a global variable in each module called “global-run-all-array” that stores an array of initially one function pointer that points to the module’s “run-all” function.  The “global-run-all-array” global variable is defined with “appending” linkage. What this does is when bitcode files get linked together by the system linker, the “global-run-all-array” will have all of the “run-all” functions appended together and put back into the “global-run-all-array” global variable.

Then there is the problem to determine the number of entries in the “global-run-all-array”.  Clasp solves that by ensuring that the last module linked in a list of modules has a two element “global-run-all-array” where the second element is NULL and by adding a second global variable called “global-epilogue”.

When a bitcode file or a shared library is loaded into Clasp, it checks for the “global-epilogue” symbol, if it finds it then it knows that the “global-run-all-array” contains a NULL terminated array of function pointers to call.   If “global-epilogue” is not present, then it knows that “global-run-all-array” contains a single function pointer.

Clasp then invokes each of the “global-run-all-array” functions one after the other and each one of them invokes the compiled functions for the top-level forms for each of the bitcode files.

This only takes a few seconds when starting up Clasp.

Note: I haven’t been actively blogging – because I’m very, very actively programming.  If you want to say hi, I’m on IRC, freenode.org #clasp almost every day.


CL Test Gridquicklisp 2016-04-21

· 24 days ago
The difference between this and previous months:

Grouped by lisp implementation first and then by library:
https://common-lisp.net/project/cl-test-grid//ql/quicklisp-2016-04-21-diff.html

Grouped by library first and then by lisp impl:
https://common-lisp.net/project/cl-test-grid//ql/quicklisp-2016-04-21-diff2.html

(Both reports show the same data, just arranged differently)

As usually, some new libraries start to fail on old lisp implementations because they need newer ASDF.

3d-vectors redefines constant to a value not eql to the previous value. clinch starts to fail on several lisps. hyperluminal-mem refers undefined variable MOST-POSITIVE-B+SIZE. rutils crashes CCL. And some other failures. There are improvements too of course.

If you're interested in some particular failure or need help investigating something, just ask in the comments or on the mailing list.

Wimpie NortjeBuildapp fails when using uncompiled libraries.

· 24 days ago

Note: I use CCL 64-bit on Linux. I have not checked this on anything else.

I discovered that Buildapp fails to build a project when the FASLs1 for some 'standard' libraries are not available. 'Standard' meaning well known, mature libraries like Alexandria.

When I started using Common Lisp I tended to use the reader macros #+ and #- to conditionally compile for development or production. Since ASDF uses file modification times instead of code dependencies to determine what to recompile it would often happen that the project's various files were compiled using different compilation conditions. This caused many mysterious bugs.

The solution to this environment mismatch is to force a recompile of the whole project. I use a two-phase process of generating a manifest and then building the application binary. The recompile is forced by deleting2 the project FASLs before each phase.

At one point I tracked an elusive bug to a library which uses conditional reader macros for conditions which differ between my development and production environments. I extended my FASL deletion to include all the Quicklisp libraries for both building phases. This caused Buildapp to fail.

By using (ql:quickload) in its verbose mode during the build process I saw that CCL emitted 'compilation failure' warnings for some libraries while generating the manifest. Many mature and often used libraries caused such warnings. Compilation completed successfully in spite of the warnings and these libraries have been used like that for years so it does not seem to be a serious problem.

During the binary creation phase Buildapp exited at the first occurrence of a 'compiler failure' warning with an error. It seems that Buildapp escalated all warnings to errors which caused it to fail.

When your own code triggers this behaviour it is useful because it helps you ship better software. However, when external libraries trigger the failure it is extremely annoying because it blocks your development effort.

The solution for making a complete build in a consistent environment is to do a full clean before generating the manifest and project-only clean before building the binary. This enables Buildapp to load the libraries while still compiling the complete set in a known environment but it requires that the environment conditions for the libraries remain constant during the manifest generation and building phases3.

  1. 'FASL' is short for 'FASt Loading'. It is a binary file containing compiled code. ASDF prefers to load code from a FASL rather than a source file when it determines that the source has not changed since being compiled.

  2. ASDF documentation provides three options for forcing a recompile: (1) The (clear-system) API call, (2) touching the system's .asd file, and (3) deleting the project FASLs.

  3. This can be a tricky requirement because some libraries use #+quicklisp which definitely changes from manifest to building.

Zach BeaneNew version of ZS3 supports AWS4 auth

· 28 days ago

I just published ZS3 1.2.8. It’s available on my website and will be in the next Quicklisp dist update in May. The main difference is support for the latest AWS authentication system. This makes ZS3 work properly with the latest AWS regions like Frankfurt and Seoul.

If you have any trouble using it, please let me know!

(This work was for a paying customer; if you are interested in specific updates and features in ZS3 or any of my other software, get in touch.)

Daniel KochmańskiCreating a project homepage with the SCLP

· 35 days ago

Introduction

In this short tutorial I'll describe how to bootstrap easily a project website. In fact that's what I did today with the Embeddable Common-Lisp website in order to provide the RSS feed and make putting there the news easier.

Additionally I'm showing here, how to create a standalone executable for coleslaw with clon after providing quicklisp independant bundle of systems.

Quick start

First clone the repository:

$ cd /home/p/ecl
$ git clone https://gitlab.common-lisp.net/dkochmanski/sclp.git website
$ cd website

Now you should adjust the appropriate files. Edit .coleslawrc (file is self-explanatory), static pages and posts.

Each file with the extension *.page is a static page. pages/main.page is an example template with a static page - don't forget to link it in the .coleslawrc's sitenav section. Exact URL of the page is declared in the file's header.

Files named *.post represent blog/news posts which appear in the RSS feed. They are indexed and accessible from the root URL. Supported file formats are markdown, html and cl-who (if enabled).

When you're done, you could just load coleslaw with your favorite CL implementation, using Quicklisp load coleslaw and call the function main on the website directory:

(ql:quickload 'coleslaw)
(coleslaw:main "/home/p/ecl/website/")

We will take more ambitious road - we'll create a standalone executable with a proper command line arguments built from a clean bundle produced by Zach Bane's Quicklisp. CLI arguments will be handled by Clon - the Command-Line Options Nuker, an excellent deployment solution created by Didier Verna.

Creating the bundle

Bundle is a self-containing tree of systems packed with their dependencies. It doesn't require internet access or Quicklisp and is a preferred solution for the application deployment.

Some dependencies aren't correctly detected - Quicklisp can't possibly know, that our plugin will depend on the cl-who system, and it can't detect cl-unicode's requirement during the build phase - flexi-streams (this is probably a bug). We have to mention these systems explicitly.

Clon is added to enable the clonification (keep reading).

(ql:bundle-systems '(coleslaw flexi-streams
                     cl-who cl-fad
                     net.didierverna.clon)
                   :to #P"/tmp/clw")

Clonifying the application

(in-package :cl-user)
(require "asdf")

(load "bundle")
(asdf:load-system :net.didierverna.clon)
(asdf:load-system :coleslaw)
(asdf:load-system :cl-fad)

(use-package :net.didierverna.clon)
(defsynopsis (:postfix "DIR*")
  (text :contents "Application builds websites from provided directories.")
  (flag :short-name "h" :long-name "help"
        :description "Print this help and exit."))

(defun main ()
  "Entry point for our standalone application."
  (make-context)
  (when (getopt :short-name "h")
    (help)
    (exit))
  (print (remainder))
  (handler-case (mapcar
                 #'(lambda (p)
                     (coleslaw:main
                      (cl-fad:pathname-as-directory p)))
                 (remainder))
    (error (c) (format t "Generating website failed:~%~A" c)))
  (terpri)
  (exit))

(dump "coleslaw" main)

You may generate the executable with sbcl and ccl (ecl has some problems with the coleslaw dependency - esrap, I'm working on it). I have used ccl, because it doesn't "derp" on the symbol exit and produces slighly smaller executable than sbcl.

Issue the following in the bundle directory (/tmp/clw):

ccl -n -l clonify.lisp

This command should create native executable named coleslaw in the same directory. On my host ccl produces binary with the approximate size 50M.

Executable usage

This is a very simple executable definition. You may extend it with new arguments, more elaborate help messages, even colors.

To generate a websites with sources in directories /tmp/a and /tmp/b you call it as follows:

./coleslaw /tmp/a /tmp/b

That's all. Deployment destination is set in the .coleslawrc file in each website directory.

Adding GIT hooks

You may configure a post-receive hook for your GIT repository, so your website will be automatically regenerated on each commit. Let's assume, that you have put the coleslaw standalone executable in place accessible with the PATH environment variable. Enter your bare git repository and create the file hooks/post-receive:

cd website.git

cat > hooks/post-receive <<EOF
########## CONFIGURATION VALUES ##########

TMP_GIT_CLONE=$HOME/tmp-my-website/

########## DON'T EDIT ANYTHING BELOW THIS LINE ##########

if cd `dirname "$0"`/..; then
    GIT_REPO=`pwd`
    cd $OLDPWD || exit 1
else
    exit 1
fi

git clone $GIT_REPO $TMP_GIT_CLONE || exit 1

while read oldrev newrev refname; do
    if [ $refname = "refs/heads/master" ]; then
        echo -e "\n  Master updated. Running coleslaw...\n"
        coleslaw $TMP_GIT_CLONE
    fi
done

rm -rf $TMP_GIT_CLONE
exit
EOF

That's all. Now, when you push to the master branch your website will be regenerated. By default .gitignore file lists directory static/files as ignored to avoid keeping binary files in the repository. If you copy something to the static directory you will have to run coleslaw by hand.

Conclusion

Coleslaw is a very nice project simplifying managing project website with easy bootstrapping the site without any need to maintain working lisp process on the server (this is static content which may be served with nginx or apache) and allowing easy blogging (write a post in markdown and push to the repository).

Sample Common-Lisp Project is a pre-configured website definition with a theme inspired by the common-lisp.net projects themes with some nice features, like RSS feed and blog engine (thanks to coleslaw).

We have described the process of creating a simple website, creating a standalone executable (which may be shared by various users) and chaining it with git hooks.

References

ECL NewsNew website look

· 35 days ago

I've imported the old archives and genearated ECL website with help of the coleslaw and the sclp. Now we have a proper RSS feed and posting news is less annoying then before.

For posterity, here is the ugly hack I've used to import archives from JSON:

(defparameter *archives-template*
  ";;;;;
title: ~A
tags:
date: ~A
author: ~A
format: md
;;;;;

~A")

(setf *json-posts*
  (with-open-file (f #P"/home/jack/linki/repo/ecl-website/static/files/misc/news-ecl-backup-2015-08-25.json"
                     :direction :input
                     :external-format '(:line-termination :cr :character-encoding :utf-8))
    (cl-json:decode-json f)))

(mapcar (let ((cnt 0))
          #'(lambda (post)
              (with-open-file (f (format nil "/tmp/archives/archive-~A.post" (incf cnt))
                                 :direction :output
                                 :if-exists :supersede
                                 :external-format (make-external-format :line-termination :unix))
                (format f *archives-template*
                        (cdr (assoc :title post))
                        ;; (cdr (assoc :labels post))
                        (substitute #\- #\/
                                    (subseq (cdr (assoc :url post)) 40 47))
                        (let ((author (cdr (assoc :author post))))
                          (if (string-equal author "dkochmanski")
                              "jackdaniel" author))
                        (remove #\Return (cdr (assoc :text post)))))))
        (cdar *json-posts*))

You may find a guide how to use the Sample Common Lisp Project template for your own project here. The clnet theme is inspired by the css in most of the common-lisp.net projects.

Best regards, Daniel

Quicklisp newsApril 2016 Quicklisp dist update now available.

· 35 days ago
Quicklisp's 67th monthly update is now available!

 Thank you to all the people who signed up for the recurring Supporter Club in the last month. The "big" fundraiser is still in the works, and I'll let you know more when there's more info to share.

New projects:
  • caveman2-widgets — Weblocks like widgets for caveman2. — LLGPL
  • cl-gamepad — Bindings to libstem_gamepad, allowing the handling of gamepad input. — Artistic
  • cl-geos — A CFFI wrapper of GEOS for performing geometric operations in Lisp. — Lisp-LGPL
  • cl-hash-table-destructuring — Hash table destructuring utils — WTFPL
  • cl-statsd — Statsd client in Common Lisp — MIT
  • cl-vhdl — My attempt to understand VHDL, and basicly make VHDL with Lisp-macro — MIT
  • electron-tools — Download, extract, and run Electron binaries. — MIT
  • flare — Easy particle systems with fine grained control. — Artistic
  • inlined-generic-function — MOP implementation of the fast inlinable generic functions dispatched in compile-time — LLGPL
  • liblmdb — Low-level LMDB bindings. — MIT
  • lmdb — Bindings to LMDB. — MIT
  • oclcl — oclcl is a library S-expression to OpenCL C. — LLGPL
  • prbs — A library of higher-order functions for generating Pseudo-Random Binary Sequences of (practically) any degree — MIT
  • prometheus.cl — Prometheus.io Common Lisp client — MIT
  • random-state — Portable random number generation. — Artistic
  • remote-js — Send JavaScript from Common Lisp to a browser. — MIT
  • sketch — Sketch is a Common Lisp framework for the creation of electronic art, computer graphics, visual design, game making and more. It is inspired by Processing and OpenFrameworks. — MIT
  • tm — Formalized Iteration Library for Common LISP — MIT
  • trivial-compress — Compress a directory. — MIT
  • trivial-string-template — A trivial string template library, inspired by Python's string.Template — MIT
  • trivial-ws — Trivial WebSockets. — MIT
Updated projects3d-vectorsalexandriaarchitecture.service-providerarrow-macrosasdf-flvasteroidsbinfixburgled-batteriesceramiccl+sslcl-anacl-asynccl-autowrapcl-bsoncl-geometrycl-hash-utilcl-itertoolscl-jpegcl-l10ncl-lexercl-llvmcl-marklogiccl-mockcl-mtgnetcl-mysqlcl-ohmcl-openglcl-opsresearchcl-pangocl-rabbitcl-rethinkdbcl-sdl2cl-slugcl-string-matchcl-stringscl-tasuketecl-tetris3dcl-wordcutcl-yaclyamlclack-errorsclassimpclinchcloser-mopclxcommon-doccommon-doc-plumpcommon-htmlcommonqtcopy-directorycroatoandartsclemailaddressdeedsdefpackage-plus,dissectdocparseresrapesrap-liquidfare-utilsfast-ioform-fiddlegendlhyperluminal-memjp-numeralkenzolakelisp-interface-librarylocal-timemacrodynamicsmcclimmitonorthosicatpaiprolog,parse-jspath-parseprojecturedqtoolsqtools-uiquickutilrpmrtg-mathrutilssafe-queuescalplsdl2kitserapeumsimple-date-timesimple-tasksskittersmugsnarksouthspinneretstaplestumpwmsxql,teepeedee2temporal-functionstriviatrivial-channelstrivial-extractusocketutilities.print-treewhichworkout-timer.

To get this update, use (ql:update-dist "quicklisp").


Michael MalisHow to Generate Self-Referential Programs

· 36 days ago

In this post, I am going to show you how to write programs that are self-referential. By self-referential, I mean programs which are able to obtain their own source code without any external input. In other words, they won’t just read from their own files. This post is based on section 6.1 of the book Introduction to the Theory of Computation.

Before we can start generating self-referential programs we are first going to need some techniques for generating programs in general. The first technique we need is a method of taking a given program and writing a second program that outputs the given program. As an example, given (+ 2 2), we would need to write a program that outputs (+ 2 2). In most languages this is easy. One way to do it in Lisp is to put a quote in front of the program:

'(+ 2 2)
=> (+ 2 2)

We are also going to need a function that automates this process. Such a function would take a program as its argument and return a new program that when ran, outputs the program that was originally passed to the function. In most languages doing this is fairly tricky. In Lisp, we can write this function easily through backquote:

(defun code-that-generates (program)
  `',program)

(code-that-generates '(+ 2 2))
=> '(+ 2 2)

If you don’t understand how backquote works, you can read this. Even though it’s for Emacs Lisp, everything there is still applicable to other Lisps. Just make sure that you understand that code-that-generates can be used to generate a program that outputs a given program.

Now that we have these two techniques, we can begin writing programs that are able to refer to themselves. The first self-referential program we will write will be an example of a quine. If you don’t know, a quine is a program that outputs its own source code. The quine we are going to write is made up of two parts, part A and part B, where part A is a function that is applied to part B:

(A B)

To describe how the quine works, it is easiest to start with part B. All that part B needs to do is return the source code of part A:

(A 'A)

Part A’s job is to take its own source code, and use it to obtain the source code of the entire quine. Since B is a program that outputs A, A can use code-that-generates on its own source code in order to obtain the source code of B. Once A has the source code of both A and B, it becomes trivial to combine the two to obtain the source code of the entire quine. Here is the complete quine, with the call to code-that-generates inlined:

((lambda (a)
   (let ((b `',a))
     `(,a ,b)))
 '(lambda (a)
    (let ((b `',a))
      `(,a ,b))))
=>
((lambda (a)
   (let ((b `',a))
     `(,a ,b)))
 '(lambda (a)
    (let ((b `',a))
      `(,a ,b))))

Now this is where things start getting interesting. A quine can be thought of as a program that generates its own source code, and immediately returns it. What if instead of immediately returning its own source code, the quine applied a function to it first, and then returned the result of that. The steps for building such a program are almost exactly the same as the steps we took for building the quine. This time, there is a third part F, for the function we want to call. The structure of the program will look like the following:

(F AB)

Where AB has a similar structure to our quine. After breaking AB into the two parts, A and B, the program looks like the following:

(F (A B))

Part B in the above program has the same responsibilities as B in the quine, it returns the source code for A:

(F (A 'A))

Then once A has the source code for itself, it can use code-that-generates to obtain the source code for B. Now that it has the source of A and B, it is easy for it to construct AB. Once part A has the code for AB, it can easily generate the source of the entire program. Here is what the program becomes after filling in everything except F:

(F
 ((lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `(F ,ab))))
  '(lambda (a)
     (let ((b `',a))
       (let ((ab `(,a ,b)))
         `(F ,ab))))))

What makes this so awesome is that F can be any function we want, and the above program will run F with the source code of the entire program! For example, replacing F with identity causes the program to become a quine:

(identity
 ((lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `(identity ,ab))))
  '(lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `(identity ,ab))))))
=>
(identity
 ((lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `(identity ,ab))))
  '(lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `(identity ,ab))))))

But we can also do some much more impressive things. We can replace F with a function that lists its argument twice, and get a program that returns a list containing its own source code twice:

((lambda (x) (list x x))
 ((lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `((lambda (x) (list x x)) ,ab))))
  '(lambda (a)
     (let ((b `',a))
       (let ((ab `(,a ,b)))
         `((lambda (x) (list x x)) ,ab))))))

=>

(((lambda (x) (list x x))
  ((lambda (a)
     (let ((b `',a))
       (let ((ab `(,a ,b)))
         `((lambda (x) (list x x)) ,ab))))
   '(lambda (a)
      (let ((b `',a))
        (let ((ab `(,a ,b)))
          `((lambda (x) (list x x)) ,ab))))))
 ((lambda (x) (list x x))
  ((lambda (a)
     (let ((b `',a))
       (let ((ab `(,a ,b)))
         `((lambda (x) (list x x)) ,ab))))
   '(lambda (a)
      (let ((b `',a))
        (let ((ab `(,a ,b)))
          `((lambda (x) (list x x)) ,ab)))))))

To make writing these self-referential programs easier, we can define a function that fills in F for us. It just requires a little nested backquote trickery.1

(defun self-referential-version-of (f)
  `(,f
     ((lambda (a)
        (let ((b `',a))
          (let ((ab `(,a ,b)))
            `(,',f ,ab))))
       '(lambda (a)
          (let ((b `',a))
            (let ((ab `(,a ,b)))
              `(,',f ,ab)))))))

(self-referential-version-of '(lambda (x) (list x x))
=>
((lambda (x) (list x x))
 ((lambda (a)
    (let ((b `',a))
      (let ((ab `(,a ,b)))
        `(,'(lambda (x) (list x x)) ,ab))))
  '(lambda (a)
     (let ((b `',a))
       (let ((ab `(,a ,b)))
         `(,'(lambda (x) (list x x)) ,ab))))))

Now that we’ve got a function that can generate self-referential programs for us, I am going to show you how to build something called a quine-relay. A quine-relay is like a normal quine, except it passes through multiple languages. The quine-relay we are going to write is a Lisp program that outputs a C program that outputs the original Lisp program. All we have to do is write a function that takes its argument and writes a C program that prints the argument it was given. Then we can pass that function to self-referential-version-of to get the quine-relay! That’s it! Here is a program that will generate the quine-relay:

(self-referential-version-of
  '(lambda (self)
     (format t

"#include <stdio.h>~%int main(){printf(\"%s\",~(~s~));}"

             (remove #\newline (prin1-to-string self)))))

I’ve omitted the actual quine-relay for brevity, but you can find it here if you are curious. There are a few idiosyncrasies in the above program and in the quine-relay because of the differences in behavior between Lisp and C. For example, in C you can’t have multi-line strings, so it becomes easier to remove all of the newlines from the Lisp program, than it is to keep them.

And that’s all it takes to write self-referential programs. After seeing how easy it is to generate a quine-relay, it shouldn’t be hard to imagine how to write one with many more steps. You may even be able to get up to 100 if you work at it long enough.

The post How to Generate Self-Referential Programs appeared first on Macrology.

Wimpie NortjeKeep Quicklisp and Qlot out of your application binary.

· 43 days ago

'How do I create a Lisp application binary without including Quicklisp or Qlot?'

Quicklisp helps you work faster because it knows where to find libraries and Qlot keeps you mostly out of dependency hell. Without these two tools application development would be dead slow. However, applications distributed as standalone binaries should not contain them.

Quicklisp adds unnecessary code and it will likely try to create a ~/quicklisp directory on your user's machine. This can fail for any number of reasons (such as file permissions or lack of internet access) which will only cause headaches.

Qlot also adds unnecessary code and it will cause the same problems as Quicklisp.

The process of building a binary using Buildapp and Quicklisp without actually having them inside the final application is as follows:

  1. Load your project using the normal Quicklisp method, i.e. (ql:quickload).
  2. Export a manifest file which lists the absolute path to every ASDF system currently loaded into the Lisp image. This is done using (ql:write-asdf-manifest-file).
  3. Exit from Lisp.
  4. Use Buildapp to create your binary. The manifest file must be passed as a parameter, --load-system must be used to load your system and Quicklisp must NOT be loaded.

@xach explained the procedure in this Stack Overflow answer.

When Qlot is employed in a project, the above process becomes:

  1. Load Qlot.
  2. Load your project using Qlot's method, i.e. (qlot:quickload).
  3. Export the manifest file using (qlot:with-local-quicklisp (ql:write-asdf-manifest-file)).
  4. Exit from Lisp.
  5. Use Buildapp to create your binary.

Since Quicklisp is not aware of Qlot (ql:write-asdf-manifest) must be wrapped with (qlot:with-local-quicklisp) in order to generate paths to the project-local Qlot managed libraries instead of the system wide Quicklisp managed libraries.

Example

This is an excerpt of a makefile from a project which uses Qlot. The makefile is used to create a standalone binary that does not contain Quicklisp or Qlot. The prep-quicklisp.lisp script is used to setup Quicklisp for loading the project system from an arbitrary location.

# CCL Flags for manifest build
MANIFEST_FLAGS =  --no-init 
MANIFEST_FLAGS += --batch 
MANIFEST_FLAGS += --load prep-quicklisp.lisp
MANIFEST_FLAGS += --eval '(ql:quickload :qlot)'
MANIFEST_FLAGS += --eval '(qlot:install :$(QL_SYSTEM))'
MANIFEST_FLAGS += --eval '(qlot:quickload :$(QL_SYSTEM))'
MANIFEST_FLAGS += --eval '(qlot:with-local-quicklisp :$(QL_SYSTEM) (ql:write-asdf-manifest-file \#P"$(MANIFEST)" :if-exists :supersede :exclude-local-projects nil))'
MANIFEST_FLAGS += --eval '(quit)'

# Buildapp settings
B_FLAGS =  --output $(OUTDIR)/$(TARGET)
B_FLAGS += --manifest-file $(MANIFEST)
B_FLAGS += --load-system $(QL_SYSTEM)
B_FLAGS += --entry app:main

make_manifest: 
	$(LISP) $(MANIFEST_FLAGS)

make_app: 
	$(BUILDAPP) $(B_FLAGS) 

Michael MalisLoops in Lisp Part 4: Series

· 43 days ago

This is part four of Loops in Lisp. Follow one of the following links for part one, two, or three).

One of the many advantages of programming in a functional style (by this, I mean manipulating your data through the operations, map, fold, and filter) is that your program winds up being made up a bunch of tiny and composable pieces. Since each piece is so small, usually only a few lines each, it becomes trivial to unit test the entire program. Additionally, it is easy to express new features as just the composition of several existing functions. One disadvantage of programming through map and friends, is that there is fairly large time penalty for allocating the intermediate results. For example, every time filter is called on a list, a new list needs to be allocated. These costs add up pretty quickly and can make a functional program much slower than its imperative equivalent.

One solution to this problem is laziness. Instead of allocating a new list every time an operation is performed on a list, you instead keep track of all of the transformations made on the list. Then when you fold over the list, you perform all of the transformations as you are folding over it. By doing this, you don’t need to allocate intermediate lists. Although laziness doesn’t allocate any intermediate lists, there is still a small cost for keeping track of the laziness. An alternative solution that makes functional programming just as fast as imperative programming is provided by the Series library.1 Series lets you write your program in a functional style without any runtime penalty at all!

Personally, the Series library is my favorite example of the magic that can be pulled off with macros. In short, Series works by taking your functional code and compiling it down into a single loop. In this loop, there is one step per transformation performed on the original list. The loop iterates over the values of the original sequence on at a time. On each iteration, the loop takes a single element, performs all of the transformations performed on the list on that single element, and then accumulates that value into the result according to the folding operation. This loop requires no additional memory allocation at runtime, and their is no time penalty either! As an example, here is a program that sums the first N squares, written using Series:

(defun integers ()
  "Returns a 'series' of all of the natural numbers."
  (declare (optimizable-series-function))
  (scan-range :from 1))

(defun squares ()
  "Returns a 'series' of all of the square numbers."
  (declare (optimizable-series-function))
  (map-fn t 
          (lambda (x) (* x x)) 
          (integers)))

(defun sum-squares (n)
  "Returns the sum of the first N square numbers."
  (collect-sum (subseries (squares) 0 n)))

(sum-squares 10)
=> 385

The above code certainly looks functional, there are no side effects in sight. Now let’s look at the code generated by Series. Here is what the macroexpansion of collect-sum looks like:

(common-lisp:let* ((#:out-969 n))
  (common-lisp:let ((#:numbers-966
                     (coerce-maybe-fold (- 1 1) 'number))
                    #:items-967
                    (#:index-965 -1)
                    (#:sum-959 0))
    (declare (type number #:numbers-966)
             (type (integer -1) #:index-965)
             (type number #:sum-959))
    (tagbody
       #:ll-970
       (setq #:numbers-966
             (+ #:numbers-966
                (coerce-maybe-fold 1 'number)))
       (setq #:items-967
             ((lambda (x) (* x x)) #:numbers-966))
       (incf #:index-965)
       (locally
          (declare (type nonnegative-integer #:index-965))
         (if (>= #:index-965 #:out-969)
             (go end))
         (if (< #:index-965 0)
             (go #:ll-970)))
       (setq #:sum-959 (+ #:sum-959 #:items-967))
       (go #:ll-970)
     end)
    #:sum-959))

What series does it looks at the entire lifetime of the sequence from its creation until it is folded. It uses this information to build the above loop which simultaneously generates the original sequence, maps over it, filters elements out of it, and folds it into the final result. Here is the breakdown of the expansion. Lines 1-9 are just initialization. They define all of the variables the loop will be using and set them to their starting values. The important variables to keep track of are #:NUMBERS-966, #:ITEMS-967, and #:SUM-959. As the code “iterates” over the original sequence, #:NUMBERS-966 is the value of the original sequence, #:ITEMS-967 is the square of that value, and #:SUM-959 is the sum of the squares so far. The rest of the code is the actual loop.

The loop first takes #:NUMBERS-966, the previous value of the sequence, and increments it in order to set it to current value of the sequence (since the sequence is the range from 1 to infinity). Next the loop takes the square of #:NUMBERS-966 to get the ith square number and stores that in #:ITEMS-967. Then the loop checks if it ha taken more than N elements out of the sequence, and if so, terminates. Finally the loop takes the value in #:ITEMS-967 and accumulates that into #:SUM-959.

Although the imperative version is equivalent to the original functional code, it is much faster than the functional code if the functional code were to allocate intermediate results or use laziness. This idea of turning transformations on a list into a loop doesn’t just work for this simple example, it also works for much more complicated programs. I just find it incredible that Series is able to take such pretty code and compile it into code that is extremely fast.

The post Loops in Lisp Part 4: Series appeared first on Macrology.

LispjobsFRONT-END DEVELOPER (CLOJURESCRIPT), Vital Labs, San Francisco

· 45 days ago

http://vitallabs.co/jobs/full-stack.html

FRONT-END DEVELOPER (CLOJURESCRIPT)

We are looking for a generalist developer with a front-end focus and strong interest in working with the Clojure ecosystem who can lead or contribute to all aspects of a modern technology stack. Our production systems are built almost entirely in Clojure/Clojurescript with help from Java/Javascript libraries as needed. We leverage Cassandra and Datomic as our data storage infrastructure and orchestrate all these tools with Ansible. We build our web interfaces with React, as well as our current mobile interfaces. We will be expanding our platforms into native iOS/Android and are exploring new tools such as React Native.

We emphasize simplicity and elegance to combat the inherently complex nature of healthcare. If you are a jack-of-all-trades with a deep interest in building front-end systems that involve complex client-server IO, data visualization, and helping people make sense of machine learning dat, then we'd love to talk to you.

YOU SHOULD HAVE

  • 4+ years working on front-end systems (desktop or mobile).
  • 2+ years working on production distributed systems projects with strong exposure to the back-end.
  • Experience working with UX and UI designers.
  • Strong knowledge of web standards, cross-browser issues, and CSS
  • Comfortable with one or more dynamic languages such as Python, Ruby, or Clojure.

IT'D BE GREAT IF YOU HAD

  • Comfort working with React or React Native
  • Experience with data visualization or animation in a web context
  • A track record contributing to open source software

OTHER STUFF THAT IS VERY RELEVANT

  • Experience with the Java/Clojure ecosystem
  • Exposure to Healthcare IT technologies and challenges
  • Exposure to AI – expert systems, statistical modeling, etc.
  • A UX/UI design background and/or interest

Fernando BorrettiUsing LMDB from Common Lisp

· 50 days ago

LMDB is a fast key-value store. This talk is useful for those who want to learn more. The design of LMDB means many of the things that are standard in other databases - write-ahead logs, and all the filesystem housekeeping necessary to implement concurrent transactions - is unnecessasry in LMDB.

The bindings are implemented as two separate libraries: liblmdb, a low-level, autogenerated CFFI binding; and lmdb, the high-level CLOS binding.

Usage

Using LMDB requires some work. A simple query requires setting up (and tearing down) a whole stack of objects, namely:

  1. An environment, which is, essentially, a collection of databases. You create the environment object by passing a directory where LMDB will store its data.
  2. A transaction within that environment. All queries have to take place inside a transaction.
  3. A database access object, which is created from a transaction, after the transaction's been started. The database object keeps the name of the database we're accessing within the environment.

Or,

LMDB lifecycle diagram

When you have the database object, you can set, retrieve and delete key-value pairs. For more complex operations, you have to use cursors, which add another level of lifecycle management within databases.

Examples

Starting by loading LMDB and Alexandria,

CL-USER> (ql:quickload '(:lmdb :alexandria))
To load "lmdb":
  Load 1 ASDF system:
    lmdb
; Loading "lmdb"
.............
To load "alexandria":
  Load 1 ASDF system:
    alexandria
; Loading "alexandria"

(:LMDB :ALEXANDRIA)

We'll store the database in your home directory under lmdb-test/, and use a hardcoded named LMDB database:

CL-USER> (defparameter +directory+
           (merge-pathnames #p"lmdb-test/" (user-homedir-pathname)))
+DIRECTORY+

CL-USER> (defparameter +db-name+ "mydb")
+DB-NAME+

First, let's abstract away all of the housekeeping:

CL-USER> (defmacro with-db ((db) &body body)
           (alexandria:with-gensyms (env txn)
             `(let ((,env (lmdb:make-environment +directory+)))
                (lmdb:with-environment (,env)
                  (let ((,txn (lmdb:make-transaction ,env)))
                    (lmdb:begin-transaction ,txn)
                    (let ((db (lmdb:make-database ,txn +db-name+)))
                      (lmdb:with-database (,db)
                        (prog1
                          (progn
                            ,@body)
                          (lmdb:commit-transaction ,txn)))))))))
WITH-DB

We can retrieve keys using the get function:

CL-USER> (with-db (db)
           (lmdb:get db #(1)))
NIL

Obviously this returns NIL, since we haven't actually set anything. To add or overwrite a key value pair, you use put:

CL-USER> (with-db (db)
           (lmdb:put db #(1) #(1 2 3)))
#(1 2 3)

CL-USER> (with-db (db)
           (lmdb:get db #(1)))
#(1 2 3)

That's better. But raw byte vectors are unwieldy: how can we store actual data?

First, let's get rid of this key/value pair so we can get back to a blank slate. We use the del function for that:

CL-USER> (with-db (db)
(lmdb:del db #(1))) T

CL-USER> (with-db (db)
           (lmdb:get db #(1)))
NIL

Alright, so, real data. These bindings only handle byte vectors: fancier datatypes are explicitly anti-features. Serialization of more complex data structures to byte vectors should be done by a higher-level library - maybe I'll write a Moneta clone for Common Lisp.

Storing strings is pretty simple, all you need is the trivial-utf-8 library:

CL-USER> (ql:quickload :trivial-utf-8)
To load "trivial-utf-8":
  Load 1 ASDF system:
    trivial-utf-8
; Loading "trivial-utf-8"

(:TRIVIAL-UTF-8)

CL-USER> (defun str->vec (str)
           (trivial-utf-8:string-to-utf-8-bytes str))
STR->VEC

CL-USER> (defun vec->str (vec)
           (trivial-utf-8:utf-8-bytes-to-string vec))
VEC->STR

Now we can use this like this:

CL-USER> (with-db (db)
           (lmdb:put db (str->vec "Common Lisp")
                        (str->vec "An ANSI-standarized Lisp dialect")))
#(65 110 32 65 78 83 73 45 115 116 97 110 100 97 114 105 122 101 100 32 76 105
  115 112 32 100 105 97 108 101 99 116)

CL-USER> (with-db (db)
           (vec->str (lmdb:get db (str->vec "Common Lisp"))))
"An ANSI-standarized Lisp dialect"

How about integers? We use bit-smasher for that:

CL-USER> (ql:quickload :bit-smasher)
To load "bit-smasher":
  Load 1 ASDF system:
    bit-smasher
; Loading "bit-smasher"
...
(:BIT-SMASHER)

CL-USER> (defun int->vec (int)
           (bit-smasher:int->octets int))
INT->VEC

CL-USER> (defun vec->int (vec)
           (bit-smasher:octets->int vec))
VEC->INT

And usage:

CL-USER> (with-db (db)
           (lmdb:put db (str->vec "Common Lisp/age")
                        (int->vec 21)))
#(21)

CL-USER> (with-db (db)
           (vec->int (lmdb:get db (str->vec "Common Lisp/age"))))
21

This works with Common Lisp's arbitrary-precision integers, as well. Let's try ten to the three hundredth power1:

CL-USER> (expt 10 300)
1e300

CL-USER> (integer-length *)
997

Nine hundred and ninety seven bits is larger than the average machine word, and will be until we start dismanting planets into computers2. Let's see how it works:

CL-USER> (with-db (db)
           (lmdb:put db (str->vec "big integer")
                        (int->vec (expt 10 300))))
#(23 228 60 136 0 117 155 165 156 8 225 76 124 215 170 216 106 74 69 129 9 249
  28 33 197 113 219 232 77 82 217 54 244 74 190 138 61 91 72 193 0 149 157 157
  11 108 200 86 179 173 201 59 103 174 168 248 224 103 210 200 208 75 193 119
  247 180 40 122 110 63 205 163 111 163 179 52 46 174 180 66 225 93 69 9 82 244
  221 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
  0 0)

CL-USER> (with-db (db)
           (vec->int (lmdb:get db (str->vec "big integer"))))
1e300

So all of this is fine, but what if we don't know the contents of the database? That's what cursors are for, but we don't need to deal with them directly because this wrapper abstracts them:

CL-USER> (with-db (db)
           (lmdb:do-pairs (db key value)
             (format t "~A: ~A~%~%" key value)))
#(67 111 109 109 111 110 32 76 105 115 112): #(65 110 32 65 78 83 73 45 115 116
                                               97 110 100 97 114 105 122 101
                                               100 32 76 105 115 112 32 100 105
                                               97 108 101 99 116)

#(67 111 109 109 111 110 32 76 105 115 112 47 97 103 101): #(21)

#(98 105 103 32 105 110 116 101 103 101 114): #(23 228 60 136 0 117 155 165 156
                                                8 225 76 124 215 170 216 106 74
                                                69 129 9 249 28 33 197 113 219
                                                232 77 82 217 54 244 74 190 138
                                                61 91 72 193 0 149 157 157 11
                                                108 200 86 179 173 201 59 103
                                                174 168 248 224 103 210 200 208
                                                75 193 119 247 180 40 122 110
                                                63 205 163 111 163 179 52 46
                                                174 180 66 225 93 69 9 82 244
                                                221 16 0 0 0 0 0 0 0 0 0 0 0 0
                                                0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
                                                0 0 0 0 0 0 0 0 0)

NIL

Which is not very informative, since these are just byte vectors.

Finally, you don't want to keep the database directory:

CL-USER> (uiop:delete-directory-tree +directory+ :validate t)
#P"/home/eudoxia/lmdb-test/"

Footnotes

  1. I replaced the actual integer representation from the REPL with 1e300 for brevity.

  2. A 1024-bit wide machine word is probably overkill even then.

Wimpie NortjeExplaining version priority handling in Qlot.

· 50 days ago

How do I specify a library version that is newer than the specified Quicklisp distribution?

While struggling to match a database, Linux libraries, database drivers and all the correct Quicklisp library versions one question I struggled a lot with was 'How do I specify a library version that is newer than the specified Quicklisp distribution?'

The Qlot documentation says about library priorities: 'If multiple distributions provide the same library, lower one would take priority over higher ones.'

This can be interpreted in more than one way which can lead to confusion. The correct interpretation is that the 'lower one' in the documentation refers to the order of the declarations in the qlfile.

To explain Qlot's priority handling more clearly: The order of the declarations in qlfile determines the priority. When multiple distributions provide the same functionality, later statements override the the earlier ones.

The two examples demonstrate the Qlot priority handling.

Using Clack from the latest Quicklisp distribution.

ql :all 2014-01-13
ql clack :latest

Using Clack from the 2014-01-13 distribution.

ql clack :latest
ql :all 2014-01-13

Wimpie NortjeFree your project from dependency hell.

· 57 days ago

'How do you manage libraries when different versions of same one is used by different projects?'

It is possible to override a library in Quicklisp's release distribution by placing the desired version in quicklisp/local-projects/ or by ensuring that it is present in ASDF's load path.

One can implement some scheme to override the required libraries in order to set up a Lisp environment with all the correct library versions for each project. This will be time consuming and error prone.

The easy solution to this problem is to use Qlot.

The easy solution to this problem is to use Qlot. It is a dependency management tool built on Quicklisp for Quicklisp libraries. It installs and maintains a separate Quicklisp installation independent from the main installation. One can specify the source and version for each library individually. Unspecified libraries are loaded from the project's default Quicklisp repository, which itself can be specified.

Projects which do not need dependency management simply use Quicklisp as before without even being aware of the existence of Qlot.

Library dependencies are specified in a qlfile and the project system is loaded much like plain Quicklisp.

Qlfile

# "qlfile" of "myapp"
git clack https://github.com/fukamachi/clack.git
github datafly fukamachi/datafly :branch v0.7.x
ql log4cl 2014-03-17

Loading a system

;; Installing libraries project-locally.
(qlot:install :myapp)

;; Loading a project with its project-local quicklisp.
(qlot:quickload :myapp)

By using Qlot in your projects you can guarantee that it will build with the correct libraries irrespective of the build time or place.

Wimpie NortjeUse Quicklisp to load personal projects from arbitrary locations.

· 60 days ago

'How does one load a personal project using Quicklisp?'

That is a question which keeps on popping up even though it has been answered many times.

The answers usually involve moving your project to quicklisp/local-projects/, use symlinks from local-projects/ to your system or modifying ASDF search paths to include your custom location.

I suspect people keep on asking the question because the usual recommendations have one or more of the following problems:

  1. Programmers have their own methods to organize code. They don't want to move their code around to accommodate their tools.

  2. Successfully building a project should not depend on the source code being in a specific location.

  3. Building a project on a new computer should not require non-standard environment setups.

  4. It is not possible to work on multiple branches of the same project in parallel if the branches are all located in local-projects/.

  5. ASDF is a lower level tool than Quicklisp. Messing with the ASDF functionality on which Quicklisp depends has the potential to cause problems later.

It is possible to load an ASDF system from any arbitrary location and to avoid all these problems caused by the other methods with the example code below.

(pushnew (truename "/projects/app/") ql:*local-project-directories* )
(ql:register-local-projects)
(ql:quickload :app)

Didier VernaELS 2016 registration now open!

· 64 days ago

Some people do seem to be in the starting blocks for the 9th European Lisp Symposium. One person has already booked his flight, while 3 people from Poland registered yesterday, with the web form that I was still testing. All of this, without the final programme being available, and hell, we're still missing a couple of reviews!

Thank you for the confidence! The registration page is now officially open! :-)

Zach BeaneForcing higher safety levels in SBCL

· 64 days ago

SBCL has a system to let you force compilation with high safety. It overrides any other declarations.

Imagine you have some code with some (speed 3) (safety 0) declarations, and it’s landing you in the debugger without useful variable or location info.

Calling (sb-ext:restrict-compiler-policy 'safety 3) before recompiling the code will force the compiler policy to high safety, ignoring the (safety 0) declarations.

If you use slime, the C-u prefix before compilation commands will also force high safety for the duration of that compilation. I use it for C-c C-c (slime-compile-defun) and C-c C-k (slime-compile-and-load-file) all the time. It’s a quick way to get a lot more debug info when I hit sldb.

This feature was created by Nikodemus Siivola in 2007. Thanks, Nikodemus!

Quicklisp newsRecovering from a breaking update

· 66 days ago
The March Quicklisp update has usocket 0.6.4, an update that unfortunately does not build on older versions of SBCL due to IPv6-related symbols. In response, Chun Tian quickly released usocket 0.6.4.1, which builds fine on older SBCLs.

It's only been a few days since the last Quicklisp dist release, so I'm not going to make a new one just for the usocket problem.

If you're hit by this issue, what can you do?

The best option, if available, is to upgrade to a recent SBCL, which has many new and exciting features and works well with the usocket in the latest Quicklisp release.

If that's not feasible, you can also manually get usocket 0.6.4.1 (or newer) from the usocket download page, unpack it in ~/quicklisp/local-projects/, and go from there.

Finally, you can revert to last month's Quicklisp dist. I first wrote about this in "Going back in (dist) time", but here's a short overview:

* (in-package :ql-dist-user)

* (second (available-versions (dist "quicklisp")))
("2016-02-08"
. "http://beta.quicklisp.org/dist/quicklisp/2016-02-08/distinfo.txt")

* (install-dist (cdr *) :replace t :prompt nil)
lots of output

In particular, the second element of available-versions will always be the second most-recent Quicklisp dist, so that's generally the one to use if you want to go one dist backward.

(Topic for the future: how better prerelease testing will catch these kinds of problems.)

Zach BeaneSketch looks really cool

· 66 days ago

Sketch, by Danilo Vidovic, looks pretty great. He describes it as “a Common Lisp environment for the creation of electronic art, visual design, game prototyping, game making, computer graphics, exploration of human-computer interaction and more.”

The examples make it look pretty easy to pop up a window and make colorful marks with it. That’s a great way to have a visually interesting feedback loop of development. I’m looking forward to trying it out.

Nicolas HafnerA Case for Documentation - Confession 61

· 69 days ago

header I thought I was done typing for today after spending all day writing up the documentation for North, but I guess I was wrong. Now, there's something that I've noticed every now and again when I take a peek at some of the new projects that pop up on Quicklisp.

Every so often there's one or two libraries that sound interesting or useful to me from their description. But then when I take a look at their project page, way too frequently I have to discover that there's either no README at all, it's just a template copy, or has a single, lonely paragraph out in the cold white space in it. It's also pretty common that docstrings are either completely absent, or only partially existent. This is really sad, because there's a fair chance I would have tried the library out, or in the very least kept it in mind for when I need it later.

Now, I understand, writing documentation takes time. A lot of time. And a lot of people are simply here to get their work done quickly. That's absolutely fine by me, I'm a very impatient person myself. However, when it comes to submitting a library to Quicklisp, it seems to me that the idea behind that would be that the library might prove useful to somebody else, so that they don't have to spend their time writing the same thing again.

And this is where Common Lisp's strength of rapid prototyping becomes a severe flaw, because it pushes people to simply roll their own thing again as they can then fit it perfectly to their needs. Plus, it's probably much more fun or even quicker to do than trying to grind through someone else's undocumented code, desperately trying to figure out how to use it or make it work in the first place.

Writing documentation takes a long time in part because it's hard to formalise and ratify things to fit into text so that hopefully somebody in the world can understand what the thought process was. Now imagine trying to do exactly that, but you did not actually write any part of the code that the documentation should describe. Trying to reverse-engineer the missing documentation from the code is a huge lot harder than writing documentation itself.

As such it doesn't surprise me much to find a lot of people distraught with the current library situation in Lisp, even though over a thousand of them are now readily available by a mere command. A large part of that particular pie is definitely also attributed to the fact that it's simply hard to discover libraries that would help you solve the problem you're tackling, but I cannot imagine that the insufficient amount of -or complete lack of documentation is not also a part of what deters people and makes them think there's nothing useful around.

Obviously there is a lot of useful code around, a lot of time and talent is hidden away in all the projects that were written in CL. It's simply such a shame that a lot of it is so difficult to get a handle on. So please, I implore you, take some time out of your busy schedule and write some documentation for your library before you submit it to Quicklisp. Even just a few paragraphs with a "How To" section that explains how to get the most basic task done helps tremendously to make your library more welcoming.

But even if you don't care about anyone else and simply submit your code to Quicklisp to profit off of its ease of distribution, I still implore you to write documentation- at least for your own sake. Trying to read back into the code of a library that's even just as little as a few months old without any documentation to go by is a huge headache and time-waster. Figuring out some way to reconstruct your past self's ideas and thoughts is very difficult, no matter how much you think you know yourself.

Writing good documentation goes beyond writing a README for your project however. Good and complete documentation includes docstring coverage of all definitions in your code, including those that are not exported, it includes writing not just about the surface on how to make use of your library, but also about its inner workings, how the machinery fits together and what kind of concepts and ideas were realised to make it all work, what kind of problems it aims to solve and how. I would even go so far as to say that good documentation is also the organisation of your source files, how you divide the code and spread it over files, packages, and systems, what you name each of them, and how you reference things across them. All of these things are -if done right- a huge help for anyone that attempts to gain understanding of your code.

Such a level of documentation takes a lot of effort, consideration, and time to do. However, while I know that I too have not reached this level for all of my libraries, I find that the ones I did the most work for are also the ones that I can find bugs the fastest in and have the least trouble getting back into when trying to rework or extend them.

So, please. Please consider taking some time out of your busy schedule to write some documentation.


P.s: If you're one of the people who thinks that docstrings in the definitions are horrendously cluttering up your source code and make it hard to see the forest for the trees in there, have a look at documentation-utils which aims to make it easy to define documentation outside of the associated definition forms.

Quicklisp newsMarch 2016 Quicklisp dist update now available

· 69 days ago
This update, Quicklisp's 66th, is brought to you by me! I've been fortunate to have Clozure sponsor a lot of Quicklisp work in the past, but now I'm self-employed. Working on Quicklisp takes time. In April, I'm going to try to raise a lump sum of money so I can work on a number of get-out-of-beta features, like better download security, provenance info, a manual, etc. Beyond that onetime fundraising, I'd like to enlist more regular monthly supporters for funding ongoing dist updates and maintenance. Do you think Quicklisp is worth it? I'm looking forward to finding out shortly.

If you have any feedback on fundraising, feel free to get in touch.

Back to your regularly scheduled update announcement...

New projects:
  • agm — A high-performance game math library. — MIT
  • cepl — Fast lispy way to work with OpenGL — BSD 2 Clause
  • cepl.camera — A camera implementation for CEPL — BSD 2 Clause
  • cepl.devil — A couple of helper functions to load from devil straight to cepl c-arrays or textures — BSD 2 Clause
  • cepl.sdl2 — SDL2 host for cepl — BSD 2 Clause
  • cepl.skitter — Plumbing to use skitter with cepl — BSD 2 Clause
  • cl-bunny — Common Lisp RabbitMQ client based on IOLib — MIT
  • cl-iterative — Generic iterative algorithm with multiple controls — LGPLv3
  • cl-llvm — CFFI bindings to the LLVM libraries. — MIT
  • cl-ohm — An object-hash mapping for Redis in Common Lisp — MIT
  • cl-sdl2-image — Bindings for sdl2_image using autowrap — MIT
  • cl-strings — A set of utilities for manipulating strings in CL. — MIT
  • cl-tetris3d — Yet another 3D Tetris clone — MIT (also see COPYING file for details)
  • cl-wordcut — Word segmentation tools for ASEAN languages written in Common Lisp — LLGPL
  • cl-zmq — Zero MQ 3 bindings — LGPLv3
  • dartsclemailaddress — Parsing and formatting email addresses (RFC 5322 compliant) — MIT
  • dendrite — Master package for all dendrite packages — BSD 2 Clause
  • documentation-utils — A few simple tools to help you with documenting your library. — Artistic
  • file-local-variable — File-local variable independent from ASDF — LLGPL
  • hu.dwim.bluez — Common Lisp FFI wrapper for libbluetooth, aka Bluez, which is a Linux Bluetooth stack. — BSD or Bugroff
  • hu.dwim.sdl — Common Lisp FFI wrapper for libSDL2. — BSD or Bugroff
  • lambda-gtk — Unspecified — LLGPL
  • legit — CL interface to the GIT binary. — Artistic
  • livesupport — Some helpers that make livecoding with slime/sly a little easier — BSD 2 Clause
  • magicffi — cffi interface to libmagic(3) — Simplified BSD License
  • mito — Abstraction layer for DB schema — LLGPL
  • mito-attachment — Mito mixin class for file management — LLGPL
  • mito-auth — User authorization for Mito classes — LLGPL
  • north — oAuth 1.0a server and client implementation, the successor to South. — Artistic
  • org-sampler — Extract docstrings as Emacs org-mode files — LLGPL 3.latest
  • perfpiece — CL:TIME on steroids. — MIT
  • rt-events — A simple real-time events API. — MIT
  • skitter — An event system for games — BSD 2 Clause
  • snark — The Snark Theorem Prover — MPL 1.1, see file LICENSE
  • trivialib.bdd — BDD and ZDD implementation using Trivia — LLGPL
  • what3words — Describe what3words here — BSD
Updated projectsarchitecture.service-providerarchivebinfixbirchbit-smasherbordeaux-threadsburgled-batteries.syntaxcavemanceramiccffichipzchronicitycl+sslcl-amqpcl-anacl-arrowscl-autowrapcl-charmscl-dbicl-events,cl-fusecl-gambolcl-gobject-introspectioncl-graphcl-itertoolscl-libuvcl-marklogiccl-opsresearchcl-pdfcl-quickcheckcl-rabbitcl-rethinkdbcl-sdl2cl-sdl2-ttfcl-strftimecl-tasuketecl-tgacl-xulclackclack-errorsclaviercloser-mop,clxcolleencontextlcroatoancurry-compose-reader-macroscxml-rngdeedsdelta-debugdjuladocparsereazy-projecteruditeesrapexternal-programfemlispfiltered-functionsfmtfngendlglkithu.dwim.defhu.dwim.perec,hu.dwim.quasi-quotehu.dwim.rdbmshu.dwim.syntax-sugarhu.dwim.utilhu.dwim.web-serverhunchentootia-hash-tableieee-floatsinquisitorintegralintel-hexiolibjskenzolacklakelisp-executablelisp-interface-librarylocal-time,lw-compatmcclimninglenstosicatparenscriptpathname-utilsperiodsplumpplump-sexpproc-parseqlotqt-libsqtoolsqurirtg-mathscalplsdl2kitserapeumsimple-taskssip-hashslimestmxstumpwmsxqltemporal-functions,triviatrivia.balland2006trivial-shellusocketvarjovomwoo.

Removed projects: buffalo (disappeared from github), cl-fgraph (per author's request), cl-quakeinfo (no longer builds on non-Allegro).

To get this update, use (ql:update-dist "quicklisp").

Enjoy!

Wimpie NortjeIronclad's password hashing needs initialization.

· 71 days ago

Update (2016-04-02): @abeaumont pointed out that the hashing issue has already been fixed in the Github repo. As of today Quicklisp provides Ironclad version 0.33.0 which dates back to 2014. Until Quicklisp provides an updated version the information in this post is still relevant.

Few people debate whether user passwords must be securely hashed before being stored on disk. Ironclad provides the tools to easily hash and check passwords with the PBKDF2 algorithm.

One of the basic requirements of PBKDF2 is that the salt value be obtained from a cryptographically secure pseudo-random number generator.

Ironclad's password hashing function ... does not initialize the random state ...

Ironclad's password hashing function uses the standard (random) function which is not cryptographically secure. Worse, it does not initialize the random state and it gives no warning or indication about this fact. The effect is that every time the application is started it uses the same sequence of pseudo-random numbers, i.e. after restart the same password generates the same hash.

It is possible to initialize *random-state* properly before using Ironclad's password hashing. This is still not cryptographically secure but at least the pseudo-random sequence is different after every restart which should be sufficient for general purpose credential protection. It will probably not be good enough for a targeted attack.

This code initializes the random state properly:

(defparameter *package-random-state* nil)

(defun hash (password)
  (unless *package-random-state*
    (setf *package-random-state* (make-random-state t)))
  (let* ((*random-state* (make-random-state *package-random-state*))
         (hashed (ironclad:pbkdf2-hash-password-to-combined-string
                    password)))
    (setf *package-random-state* (make-random-state nil))
    hashed))

Though Ironclad's password hashing is very easy to use, the cl-pass library makes it even easier. Cl-pass sets strong (in 2016) default parameters and it handles the random state initialization transparently.

Quicklisp newsFebruary 2016 Quicklisp download stats

· 72 days ago

Here are the top 100 downloads by raw download count.

 5607 alexandria
4586 cl-ppcre
4388 trivial-features
4119 babel
3369 split-sequence
3332 bordeaux-threads
3268 cl+ssl
3243 cffi
3208 anaphora
2725 closer-mop
2692 trivial-gray-streams
2635 trivial-garbage
2620 let-plus
2551 flexi-streams
2524 usocket
2515 cl-fad
2491 cl-colors
2382 cl-base64
2318 prove
2286 cl-ansi-text
2255 cl-utilities
2238 quri
2218 chunga
2203 local-time
2140 cl-html-parse
2113 puri
2102 iterate
1956 chipz
1873 nibbles
1871 drakma
1799 named-readtables
1763 ironclad
1612 cl-interpol
1551 md5
1520 trivial-backtrace
1517 cl-unicode
1418 slime
1343 lack
1336 clack
1330 trivial-types
1309 cl-annot
1295 cl-syntax
1208 fast-io
1161 trivial-utf-8
1134 salza2
1114 cl-json
1104 proc-parse
1092 static-vectors
1053 hunchentoot
992 rfc2388
990 jonathan
981 parse-number
965 cl-mysql
957 fast-http
916 clx
911 uiop
903 xsubseq
875 metabang-bind
865 clsql
836 smart-buffer
835 ieee-floats
829 lparallel
825 osicat
802 postmodern
770 closure-common
766 quicklisp-slime-helper
759 cxml
753 log4cl
699 optima
686 uuid
679 mcclim
672 array-utils
645 cl-reexport
644 cl-sqlite
633 trivial-indent
631 zpng
615 http-body
611 yason
609 fiveam
605 trivial-mimes
602 plump
589 swap-bytes
523 symbol-munger
512 cl-containers
505 cl-yacc
502 ningle
501 vom
501 simple-date-time
498 map-set
494 myway
490 lisp-unit
483 lquery
479 dexador
476 asdf-system-connections
473 cl-cookie
470 function-cache
466 cl-csv
466 iolib
466 metatilities-base
464 cl-dbi

Wimpie NortjeSending large files from Clack

· 73 days ago

For one of my projects I encountered the issue of sending a large file as an HTTP response from Clack.

Clack supports sending files as a response with Hunchentoot, FCGI and Wookie back-ends. If you use Toot as back-end you will have to implement your own method.

To send a file, return the file's path as a PATHNAME (#P"/path/to/file") as the response body.

The different back-ends use different methods to send a file. This has other implications which you may want to consider.

Server Method Notes
Hunchentoot HTTP Chunking
  • Optimal for large files.
  • Does not load whole file into RAM.
  • Multiple small messages.
Wookie Byte stream
  • Does not load whole file into RAM.
  • Single large message.
FCGI Array
  • Loads the whole file into RAM.
  • Single large message.
Toot DIY

Wimpie NortjeStoring Clack session information.

· 75 days ago

Clack comes with separate middleware modules for session management and for storing session information in a database. I discovered the storage middleware shortly after implementing my own version.

This post describes what I learnt about these two options. Though the code to implement this feature is minimal, it took me much too long to figure out the details necessary to do so.

Writing your own storage layer has the following advantages:

  • You can use storage not supported by cl-dbi, i.e. MySQL, PostgreSQL and SQLite.
  • You determine the table layout.

My suggestion is to use the included version. It will save you time. I only created my own version because I did not know Clack already included the necessary module.

Using Clack's storage middleware

This information is correct at least up to commit c4f3e09 (2015-10-27)

The class name is <clack-session-store-dbi> located at v1-compat/src/contrib/session/store/.

The code below creates a Clack application which handles the storage of session information completely automatically.

(clack:clackup
 (builder
  (<clack-middleware-session>
   :store (make-instance 'clack.session.store.dbi:<clack-session-store-dbi>
                         :connect-args '(:postgresql
                                         :database-name "DBNAME"
                                         :username "ROLE"
                                         :password "PASSWORD")))
  #'app))

A hash table containing the session information is available inside request handlers. It is obtained with (getf env :clack.session).

The hash table content is serialized before being stored to disk so it can be used to store any arbitrary data.

Session tracking is done using cookies which contain only a session ID. All other session information are kept server side.

Writing your own persistence middleware

The code below implements middleware for a storage layer. The actual database access is done by the model package.

(in-package :cl-user)
(defpackage sltv.session.store
  (:use :cl
        :clack.session.store))
(in-package :sltv.session.store)

(cl-syntax:use-syntax :annot)

@export
(defclass <sltv-session-store> (<clack-session-store>)
  ())

@export
(defmethod fetch ((this <sltv-session-store>) sid)
  (let* ((session (model:fetch-session-as-hashtable sid)))
    (setf (gethash :id session) sid)
    session))

@export
(defmethod store-session ((this <sltv-session-store>) sid session)
  (model:store-session sid session))

@export
(defmethod remove-session ((this <sltv-session-store>) sid)
  (model:remove-session sid))

Notes:

  • sid is the session ID generated by Clack.
  • The session hash table must contain a key ID which is set to the sid not the database record's ID field.
  • The session must be defined with (make-hash-table :test 'equal).
  • fetch obtains an existing session from the database or creates a new entry if it doesn't exist.
  • store-session stores the session hash table and sid in the database.
  • remove-session deletes the database record.

When an HTTP request is received the session middleware fetches the session for the received sid. If the request did not include an sid (i.e. no cookie) or it included an expired sid, Clack generates a new one and fetches (which should create an new record) the session.

The request handler has three option settings with which it can control some of the session middleware's actions.

:no-store
Do not store the session object. It is still created in the database and available in the request handler but the database entry is deleted before the response is returned.
:expire
Expire the session so that a new one is generated next time the user visits.
:change-id
Create a new session and populate it with the current data.

An option can be changed with the form

(setf (gethash :change-id (getf env :clack.session.options)) t)


For older items, see the Planet Lisp Archives.


Last updated: 2016-05-17 12:02