Gambit-list Juin 2009

gambit-list@iro.umontreal.ca

29 participants
47 discussions

Seekable String Ports
by Taylor Venable 13 Jui '09

13 Jui '09

Is there any way to seek through string ports? When I try to use input-port-byte-position I get this: > (call-with-input-string "asdf" (either (char/exactly #\c) (char/exactly #\s))) *** ERROR IN #<procedure #10>, "tcv-gambit-parse.scm"@66.20 -- (Argument 1) Device INPUT PORT expected (input-port-byte-position '#<input-port #11 (string)>) (I'm doubtful that input-port-byte-position would be what I want anyway if the string included characters that weren't encoded as single bytes, but that's a digression.) I'm trying to write a parser combinator library, and part of that entails some rewinding of streams for ordered-choice operations (as illustrated above). A potential alternative would be to duplicate the port's contents and use a different port for each alternative, but I am not aware of any API to do this either. Any ideas on how to accomplish this objective? I need something that works for at least string ports and device ports. My current code, for background: (define char/exactly (lambda (c) (lambda (stream) (let ((char (read-char stream))) (cond ((eof-object? char) #f) ((not (char=? char c)) #f) (else char)))))) (define either (lambda combinators (lambda (stream) (let loop ((c combinators)) (cond ((null? c) #f) ((apply (car c) (list stream)) #t) (else (loop (cdr c)))))))) As defined here, the either function will not undo the changes done by char/exactly (in the example above), thus each choice will advance the stream by one character. We could work around it here by using peek-char rather than read-char but that wouldn't scale to when either is used on functions that read large chunks of data before failing. Thanks for any ideas, -- Taylor Christopher Venable http://real.metasyntax.net:2357/

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define-syntax and loading files
by Taylor Venable 13 Jui '09

13 Jui '09

I'm having some trouble understanding the behavioural differences in this code: BEGIN FILE test-alpha.scm -------------------------------------------- (define-syntax foo (syntax-rules (xyzzy) ((_ xyzzy) "nothing happens"))) BEGIN FILE test-beta.scm --------------------------------------------- (load "test-alpha.scm") (define bar (lambda () (foo hello))) ====================================================================== If I load test-beta.scm twice, I get an error on the second load but not on the first one: > (load "test-beta.scm") "/home/taylor/cvs_public/Programs/Libraries/Scheme/test-beta.scm" > (load "test-beta.scm") *** ERROR IN %%chi-macro437, "/opt/gambit/lib/syntax-case.scm"@9135.1 -- invalid syntax (foo hello) But if I do what seems like it should be the equivalent of loading test-alpha.scm, then loading test-beta.scm I get an error on the first load of test-beta: > (load "test-alpha.scm") "/home/taylor/cvs_public/Programs/Libraries/Scheme/test-alpha.scm" > (load "test-beta.scm") *** ERROR IN %%chi-macro437, "/opt/gambit/lib/syntax-case.scm"@9135.1 -- invalid syntax (foo hello) It seems to me that loading test-beta by itself should be the same as loading test-alpha then test-beta, but it's not quite. Why is this? For what it's worth, my Gambit version string is: v4.4.4 20090611032636 amd64-unknown-openbsd4.5 "./configure --prefix=/opt/gambit --enable-single-host" Thanks, -- Taylor Christopher Venable http://real.metasyntax.net:2357/

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serialization of promises
by Darren Baker 11 Jui '09

11 Jui '09

Marc - Gambit doesn't allow automatic serialization of promises (delay/force) using object->u8vector, is this by design or otherwise? It seems I could get around this by rolling my own force and delay, but perhaps there's a good reason not to be trying to serialize such things? As an aside, I also noticed that there's a ##promise? predicate but no non-## version. Seemed a bit odd. Cheers Darren

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[ANN] Gambit-C v4.4.4 released
by gambit＠iro.umontreal.ca 11 Jui '09

11 Jui '09

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Proposed changes to makefile targets
by Marc Feeley 10 Jui '09

10 Jui '09

Currently the Gambit makefiles support these targets (and more): % make mostlyclean Removes all the files that can be regenerated using standard tools (C compiler, TeX, etc). The C files generated by gsc, and the gsi and gsc executables are not removed. % make clean Removes all the files that can be regenerated by a "make" (object files, C files generated by gsc, etc) **except** gsi and gsc. This is useful to bootstrap from the Scheme sources after gsc has been built with an initial "make bootstrap". % make realclean Like "make clean", but also removes gsi and gsc, and all the makefiles generated by the configure script. This is often confusing for newcomers because in most open-source projects a "make clean" followed by "make" usually restarts the build process from the state of the distributed sources. Currently, the Gambit makefiles will remove all the C files generated by gsc (which are distributed in the tar file), so in fact the system won't build unless the user had successfully done a "make bootstrap". To remove the confusion I'm going to rename the targets as follows: new "clean" target = old "mostlyclean" target new "realclean" target = old "clean" target + old "realclean" target The mostlyclean target will be removed. Moreover, a "make" will be equivalent to a "make bootstrap" unless the gsc-comp (Gambit compiler for bootstrapping) exists. This way, the user can get out of trouble if he does a "make realclean" after a "make". Please let me know if you have suggestions. Marc

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I/O puzzle...
by Marc Feeley 09 Jui '09

09 Jui '09

Puzzle... what's the bug in the following code? See end of message for answer. (define http-server-start! (lambda (hs stop?) (let ((server-port (open-tcp-server (list port-number: (server-port-number hs) backlog: 128 reuse-address: #t server-address: '#u8(127 0 0 1) ; on localhost interface only char-encoding: 'ISO-8859-1)))) (input-port-timeout-set! server-port 3) (accept-connections hs server-port stop?)))) (define accept-connections (lambda (hs server-port stop?) (let loop () (let ((connection (read server-port))) (if (eof-object? connection) (if (stop?) (close-input-port server-port) (loop)) (begin (if (server-threaded? hs) (let ((dummy-port (open-dummy))) (parameterize ((current-input-port dummy-port) (current-output-port dummy-port)) (thread-start! (make-thread (lambda () (serve-connection hs connection)))))) (serve-connection hs connection)) (loop))))))) . . . . . . . . Answer: the (input-port-timeout-set! server-port 3) is at the wrong place. It sets a timeout ***3 seconds in the future***. So after 3 seconds have passed all calls to read in accept-connections will not block (and lead to a tight, CPU intensive loop). The correct approach is to put the call to (input-port-timeout-set! server-port 3) just before the call to read. Puzzle #2: why did Gambit chose to define timeouts that are not relative to the moment that an I/O function is called? Marc

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ignore rest of the file
by lowly coder 09 Jui '09

09 Jui '09

foo.scm includes bar.scm in bar.scm, is there any command I cay say that will tell foo.scm to ignore the rest of the file? I don't want to commnent out all the second half of bar.scm nor do I want to put a lambda around it (complaints about define) is there someway I can access a continuation or something and jump out of the include? thanks!

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compiled modulers fun
by lowly coder 08 Jui '09

08 Jui '09

I've recently discovered how cool gambit is in the following way: I have some interpreted code, it's running kind of slow, so I compiled my code, and got an automatic 5x speed up. Yay!! Here's the problem though: foo.scm -> foo.o1, in the same directory. This is bad for one reason -- it screws up tab completion; I can no longer do things like: vim fo<TAB>; since it gets stuck at "foo." ... so is there anyway to make both compilation and load default to somethign like "foo.scm" -> _foo.o1 or .foo.o1 ? I realize I can manually hack this, but if there was a global default, that'd be really cool too (interpreting the path for load + rewriting it seems a bit hacky) Thanks!

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profiling / exceptions
by lowly coder 08 Jui '09

08 Jui '09

Here's my problem: I am running a multi threaded application on gsi. Thread X executes thunk THUNK. if THUNK throws an exception, I want to be able to use the repl to jump into thread X and see what is wrong (and have the whole interactive repl debugger at my finger tips). However, I also want to profile THUNK. Thus, before THUNK starts, I want to run (profile-start!) and when THUNK finishes (or if an exception is thrown), I want it to call (profile-stop!) Here now is the problem ... if I don't catch the exception (and allow myself to debug it at the GSI), my profiler will colelct data of me sitting at the REPl debugging. On the toher hand, if I catch the exception to call (profile-stop!), I no longer know how I can debug the exception at the REPL. How do I get around this? Thanks!

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Is gambit *just* a compiler/interpreter?
by Adrien Piérard 07 Jui '09

07 Jui '09

Hello everyone. As others here too I guess, I do not program only in Scheme, and I also keep myself informed of what happens around in the Common Lisp, Haskell or ML communities (since I have a functional programming bias). I believe that most of you are aware of the impressive fame of Haskell and its main implementation GHC, and I would even consider betting that "do it in a monad" will soon belong to the dialect of the IT marketing teams and deciders. Let's see what I think helped the buzz spread, let alone the language itself: - cabal: convenient and community friendly way to share, downloade and builp code. - Haskell platform: on click under windows, and you have a fully set up system with all-you-need-ready-to-use (c). - spare time: every single library coded by haskell users somehow ended up in the community shared code base. No need to redo what's already done. - communication: the haskell weekly news: state of the art, blogs, and IRC quotes. The community is alive and shows it to the world. I guess that the closest to this in "our" (very split) community is PLT-scheme. Yet, I think that Gambit too is somehow evolving along a bigger and bigger user base, but may benefit from more development targetting the (potential) users rathers that its speed or efficiency. =========== Suggested improvements to Gambit: - We have a dumping ground, which slowly but surely grows. I think that it is now time to reconsider doing a CPAN-like or cabal-like system for Gambit. Users/programmers should be suggested to put there any single line of once-useful code, without fearing comments regarding quality or else. If someone wants this code but finds it slow, it'll be patched… Snow has tried to do that, but portability killed i.(I gave up portabililty a while ago). - I haven't tried blackhole yet, don't know its limitations, but if it is good, let's make in part of Gambit (even as an external branch or whatever). - A better explanaition of of it diverges from pure RnRS (that is, emphasize on define-type, non-blocking IOs, and so on), and how it makes it relevent for most real-life programming tasks. - Involve the community and code the wish-list (or at least, give a guided tour of gambit's internals and of its where-is-whats) so that some may consider implementing those requests themselves. =========== Suggested improvements to Scheme: - We have #scheme on Freenode that is lively and wealthy. We have scheme.dk/planet which is lively and wealthy too (I just wished Grant could stop twittering on it and make real posts with more than 134 characters that all start like "here is ...". Grant, if you read this :P) Now, maybe a publication could be useful too, monthly at first, maybe unofficial, that sums up recent activity, from "XXX now runs on the iPhone, to "John Doe got a Scheme job at Great Compagny Inc", not forgetting Prof. Farnsworth's latest paper on continuations". I may be stating the obvious, but I felt the urge to share it (so much that I wrote this too quickly and will probably regret having sent it)… P! -- Français, English, 日本語, 한국어

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Gambit-list Juin 2009