pro July 2011

pro@common-lisp.net

33 participants
11 discussions

[pro] Fwd: Lisp and DSLs
by Ala'a Mohammad 28 Jul '11

28 Jul '11

[oops, I keep forgetting to add cl-pro email when replying.] IMHO: DSL can be made of a varying mix of abstraction, syntax and semantics. All of which can be achieved within CL using interpreter & compiler, macros, closures, reader macros, compiler macros, printing protocol and CLOS. These will help a lot, both the developer and the user. check the following examples: Corman CL Assembler DSL (check the source code for assembler.lisp and how elegantly normal x86 assembler syntax was introduced into CL code) http://www.cormanlisp.com/index.html SBCL VOPs: http://sbcl-internals.cliki.net/Adding%20VOPs http://paste.lisp.org/display/41937 GOAL: Game Object Assembly Lisp ("...intermix assembly instructions seamlessly with higher-level code...") http://www.gamasutra.com/view/feature/2985/postmortem_naughty_dogs_jak_and_… CLSQL: SQL syntax CL-Typesetting: typesetting DSL Prolog interpreter or compiler. those are the ones I remember directly when talking about DSL in common-lisp - Ala'a

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[pro] Lisp and DSLs
by Didier Verna 22 Jul '11

22 Jul '11

Dear friends, I'm starting to write a chapter for an upcoming book on domain specific languages. The chapter is called (tentatively): Extensible languages -- blurring the distinction between DSLs and GPLs GPL meaning General Purpose Language in this context ;-) My intention is to demonstrate how the task of implementing a DSL is made easier when it boils down to an extension or subset of your original GPL (hence reusing its infrastructure), instead of being a totally different language, only written on top of the other. Obviously, I'm going to illustrate this with Common Lisp, and I intend to speak of dynamicity (not only dynamic typing, but in general all things that can be deferred to the run-time), introspection, intersession, structural or procedural reflexivity, meta-object protocols (not sure about this one), macro systems and JIT-compilation. Also, more specifically to Lisp, reader macros (compiler macros maybe?), the condition system (and its ability to *not* unwind) and restarts. Right now, I would like to know if any of you have DSL "pearls", nice examples of DSLs that you have written in Lisp by using some of its features in a clever or elegant way. I would also gladly accept any point of view or comment on what's important to mention, in terms of design principle or anything else, things that I may have missed in the list above. Thank you very much in advance! -- Resistance is futile. You will be jazzimilated. Scientific site: http://www.lrde.epita.fr/~didier Music (Jazz) site: http://www.didierverna.com

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Re: [pro] Lisp and DSLs
by raito＠raito.com 22 Jul '11

22 Jul '11

Or at least learn the difference between a spreadsheet and a database... I see too many spreadsheets used as databases. Neil Gilmore raito(a)raito.com Quoting "Thomas M. Hermann" <thomas.m.hermann(a)odonata-research.com>: If people are going to rely on Excel to the extent that they do, I wish they'd at least learn VBA.

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Re: [pro] Lisp and DSLs
by Alessio Stalla 20 Jul '11

20 Jul '11

On Wed, Jul 20, 2011 at 9:21 PM, Martin Cracauer <cracauer(a)google.com> wrote: > I find that people have a wrong impression of what it means to have a > domain specific language. > > For me, one of the greatest advantages of Lisp is literal data in > code. I don't have to write a complicated parser for some external > data, I don't have to hook up a XML reader library to a bunch of > callbacks and construct a graph or tree or whatever in those callbacks > and then I have to write that graph in XML (ugh) with no programming > help at all unless I pipe it through m4. In Lisp code I just write the > graph, the entire thing, no matter how complicated. And although it > is Lisp source code it doesn't have to live in the source > distribution, I can load an external file later. > > And it gets to use all the Lisp tools I have built for my application > anyway, to help me construct that complicated data structure, without > using m4. > > That does a lof of what many people mean when they say they need a > DSL. What they really want is not to have to do a bazillion lines of > code to hook up the ability to read complex structured real-world > data. I agree, that's one of the greatest advantages of DSLs in Lisp (so called "internal" DSLs) versus "external" DSLs which seem to be getting the most mainstream attention these days, with complex tools to design parsers, editors and whatnot. Without even touching macros, the Lisp reader and printer systems already provide invaluable tools for reading and writing complex data, tools that other languages lack. Macros can then help as a little syntactic sugar, to remove some boilerplate, or to do some bookkeeping, or to move some computation to compile-time (another huge win other languages completely lack). XML, JSON, YAML etc. are so hyped because they introduce a little dynamics in otherwise mostly static languages like Java, but they come with the burden of libraries for parsing, writing, binding to objects, and have trouble expressing shared structure. Besides, in Lisp-based DSLs, it's generally easy or even trivial to escape to Lisp when needed, to use e.g. conditionals or looping, two basic programming language constructs that are lacking (and often missed) in "data-oriented" languages like XML. So, the code = data paradigm is really two-way: you can manipulate code as data, but you can also treat data as part of the code, and the latter point is often neglected. Alessio

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[pro] Fwd: Re: Lisp and DSLs
by raito＠raito.com 20 Jul '11

20 Jul '11

This may not be much of an example, but it's not only what I have, it's what got me hooked on Lisp. When I was a young lad, and because I lived not too far from Lake Geneva, I played this newfangled thing called D&D (back when it first came out. Get off my lawn). And one of the things that intrigued me was the tables (the kind where you rolled dice and looked up the results). And also being as I was learning programming (on a mainframe. There were no microcompputers. See my previous comment about lawns.) I thought about writing a table language. One where I could specify not only how many chances a particular result had (because I'd already figured out that that was better than using the dice themselves for a bell curve), but also being able to modify the tables themselves at run-time by feeding them arguments, being able to have sub-tables, detailed results, etc. But at the time all we had was Honeywell mainframe BASIC (supposedly FORTRAN was available, but we couldn't get a manual), and even the instructor didn't know anything about writing parsers, let alone languages. Fast forward, and the idea stuck with me. I mean, I'd gone to school and doubles in ECE and Comp. Sci., I should be able to do this. But I never did, because it's a very big hassle to write your own language. Especially in languages like C. So when I started using Lisp, I read up all this stuff about DSLs. Hm, I wonder if I could use Lisp to do my language. Well, half an hour and 15 lines of code later, I not only had my language, but more than I wanted. And here it is (ta da): (defmacro table (name args &rest rest) `(defun ,name (,@args) (declare (special ,@args)) (let* ((base ',(loop for x in rest collect (car x))) (results ',(loop for x in rest collect (cadr x))) (chances (loop for x in base collect (eval x))) (total (loop for x in chances sum x)) (roll (+ 1 (random total)))) ;(format t "Base:~{~a~^, ~}~%Chances:~{~a~^, ~}~%Results:~{~a~^, ~}~%total:~A roll:~A~%" ; base chances results total roll) (do ((n chances (cdr n)) (cnt 0) (item 0 (+ item 1))) ((eq n nil) nil) (setf cnt (+ cnt (car n))) (when (<= roll cnt) (return (eval (nth item results)))))))) and it's used like this (a simple example): (table my-table (added-chances) (1 "one") (1 "two") ((+ 1 added-chances) "three") ) I've done some stuff with it that's been quite a bit of fun. Like another layer of macro on top for those who think in terms of dice. The upshot is that it's a project I didn't do for 25 years because it was too big a pain. And I did it in Lisp in half an hour, including figuring out that I had to use dynamic scoping for args. I have to use dynamic scoping because the forms being eval'ed need to be able to access args, but args is not in their lexical scope (though it looks as if they are in the macro invocation -- which is the point). Neil Gilmore raito(a)raito.com

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[pro] generating documentation
by Tamas Papp 19 Jul '11

19 Jul '11

Hi, I am about to complete a revision of LLA and I thought I would write some decent documentation. I have most of the documentation in docstrings, though some of general discussions are in ;;; comments in files. I am looking for a reasonably automatic way of generating documentation (eg texinfo or HTML) from the source. I found many libraries for this on cliki, and instead of trying all of them out, I thought I would ask for advice here. Portability would be nice is not necessarily a requirement, so tools like sbcl's texinfo are fine too. However, if possible, I would like to put the documentation on the interface and the internal details in separate sections somehow. I would also be interested in including tutorial-like sections with examples. Thanks, Tamas PS.: I have searched the cl-pro and c.l.l archives and found some discussions about this question, but my impression was that a lot of new libraries appeared on the scene in the past few years.

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[pro] Is gensym used for anything except alpha-conversion in macros?
by Kazimir Majorinc 11 Jul '11

11 Jul '11

Is gensym used for anything except alpha-conversion in macros?

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Re: [pro] Is gensym used for anything except alpha-conversion in macros?
by Steve Haflich 10 Jul '11

10 Jul '11

On Jul 10, 2011 2:09 AM, "David McClain" <dbm(a)refined-audiometrics.com> wrote: > > Gensym can also be used to produce globally (session wide) unique objects. But this is no different from other objects, such as a cons or array. The primary difference between an uninterned symbol and any other object that has settable "slots" is its behavior as a form under evaluation. Arrays and most other objects self evaluate; a cons has complex interpretation as a form; but a symbol evaluates to its its current special or lexical value binding. That's why gensyms are mostly use as hygienic names in macro expansions. There are other ways of doing whar a ge.sym does. Maybe later when I'm not typing on a tiny phone keyboad i'll show one.

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[pro] LISP technology at Cisco
by Daniel Weinreb 08 Jul '11

08 Jul '11

This is a video about "LISP Technology at Cisco". http://www.youtube.com/watch?v=JIiBMZ86jZo&feature=player_embedded (It has nothing to do with Lisp, either.) :) -- Dan

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[pro] why :key arguments?
by Tamas Papp 05 Jul '11

05 Jul '11

Why do some CL library functions have :key arguments? I am asking because I am working on some statistics functions, and the design choice came up. Specifically, I can write functions like (defun quantiles (sequence quantiles &key (key #'identity)) ...) but it is a bit cumbersome. I can make my code simpler by relying on calls like (quantiles (map 'vector key vector) quantiles) but this conses a bit more. Not a major concern at the moment, but if it ever becomes one, I could just define a compiler macro to take care of forms like this and transform to something like (quantile-with-keys vector quantiles key) I also thought of defining something like (defgeneric map1 (function object) (:method (function (list list)) (mapcar function list)) ...) for the sole purpose of mapping objects to similar objects (eg lists to lists, arrays to arrays, etc) and allow it to be optimized away (like above) by compiler macros. I would appreciate advice on this. I am especially interested in the reason why some CL functions have :key arguments: is it because of efficiency, backward-compatibility/history, or something else? Thanks, Tamas

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pro July 2011