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Re: [gambit-list] strange results using values
by Arthur Smyles 23 Sep '08

23 Sep '08

I've looked into your bug comment. The additional use case that I see is your example code: (let ((v (values 1 2))) (call-with-values (lambda () v) cons)) It could be re-written as: (let ((v '(1 2))) (call-with-values (lambda () (apply values v)) cons)) I don't see what a user-visible values structure provides when the user already has cons, vectors, and records. I see the call-with-values as a way to create multi-value continuations and values as the standard way to call them. If the continuation does not accept multiple values (any continuation not created by call-with-values) then I'd like to see it behave as if you just returned one value. Unfortunately, the only way to use the current implementation of 'values' properly is to de-structure it using call-with-values. I think that is redundant since I can perform the same with a list, vector, or record. What I would like is to forget about secondary values when I use it normally, and only care about them when I explicitly request it. The only way to achieve this is a values semantics that I'm advocating. Some use cases (to name a few). 1. When the primary value is expensive to create and the secondary value is cheap and dependent on the primary value. 2. for table-ref, you can have a secondary value on whether the item was actually set or not. Arthur ----- Original Message ---- I've once written a response to someone posting this as bug in bugzilla: http://www.iro.umontreal.ca/~gambit/bugzilla/show_bug.cgi?id=63 I.e. I personally still think the "take first value if continuation only expects one value" approach is a bad idea. If you're really wanting to see that behaviour, maybe you could describe the reasons in more detail and think about the issues I've lined out above; maybe there is a way to achieve both. Christian.

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gambit + llvm
by Andrew I. Schein 23 Sep '08

23 Sep '08

Hi all - I am wondering if there are any efforts underway to port gambit to a llvm back end? Would this provide opportunity to eliminate a trampoline, at least in certain cases? -A -- web: www.andrewschein.com

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Re: [gambit-list] strange results using values
by Arthur Smyles 23 Sep '08

23 Sep '08

Not exactly, The definition of values given by the spec is: The R5RS's definition of values: (define (values . things) (call-with-current-continuation (lambda (cont) (apply cont things)))) Let's say you can have 2 types of continuations: 1. Single value continuations 2. multi-value continuations. If the current continuation is a single value continuation, then only return one value, otherwise for a multi-value continuation (created with call-with-values) send all the arguments. The behavior could then be like: (define (values . things) (call-with-current-continuation (lambda (cont) (if (mv-continuation? cont) (apply cont things) (apply cont (car things) '()))))) In the case of (values), I'd leave that unspecified. Arthur ----- Original Message ---- From: Bradley Lucier <lucier(a)math.purdue.edu> To: Arthur Smyles <atsmyles(a)earthlink.net> Cc: Bradley Lucier <lucier(a)math.purdue.edu>; Marc Feeley <feeley(a)iro.umontreal.ca>; gambit-list(a)iro.umontreal.ca Sent: Monday, September 22, 2008 11:35:51 AM Subject: Re: [gambit-list] strange results using values It sound like you want every place in the program that takes a value to check whether there are more than one value returned, and pick the "primary" one. So if you have (define (f a b) (+ a b)) (define (g a b) (values a b)) (f (g 0 1) 2) you'd want the code to f to check that g returned only a single value, strip out extra ones if it returned more than 1, perhaps signal an error if g didn't return any values, do something else? Common Lisp deals with this somehow, but I'm not sure that we want the semantics of values in Scheme to be complicated so much in able to implement such a proposal. Brad

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Re: [gambit-list] strange results using values
by Arthur Smyles 22 Sep '08

22 Sep '08

My use case for using 'values' is to pass a primary value and secondary values to a caller. If the caller can only use one value then I want it to use the primary value and discard the secondary values. So what I would like to see is: (if (values #f #f) #t #f) => #f since the primary value is false and the 'if' function can only use the primary value. As it stands now, as a caller of an api that uses 'values', I'd have to deal with it as a specialized data structure, in which case, the utility of it is very limited since I could just as well pass a vector or some other structure. I think the above semantics could be implemented and still be R5 compliant. Arthur ----- Original Message ---- From: Marc Feeley <feeley(a)iro.umontreal.ca> To: Arthur Smyles <atsmyles(a)earthlink.net> Cc: gambit-list(a)iro.umontreal.ca Sent: Sunday, September 21, 2008 7:35:59 PM Subject: Re: [gambit-list] strange results using values On 21-Sep-08, at 3:25 PM, Arthur Smyles wrote: > (if (values #f) #t #f) > > => #f > > (if (values #f #f) #t #f) > > => #t > > I was surprised to discover this. Although technically not a bug > since the scheme spec considers this situation unspecified, it makes > using multiple-values unreliable. In what way is it "unreliable"? The situation is defined as an error by the Scheme standard, which means a user cannot expect any specific behavior. Gambit handles multiple values by treating the "values" procedure as a data structure constructor (just like "vector" except with a different type tag). The exception is that when it is given a single argument it behaves like the identity function, so (values 123) = 123 . This explains why (if (values #f #f) 11 22) gives 11, just like (if (vector #f #f) 11 22) gives 11, but (if (values #f) 11 22) = (if #f 11 22) = 22 . > This affects pp as well > > (pp (values #f #f)) > > => #<unknown> What would you expect this to give? I'm not sure this is related to what you want to do, but these operations are available: > (##values? (values 11 22)) #t > (##vector->list (values 11 22)) (11 22) > (for-each pp (##vector->list (values 11 22))) 11 22 Marc

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strange results using values
by Arthur Smyles 22 Sep '08

22 Sep '08

(if (values #f) #t #f) => #f (if (values #f #f) #t #f) => #t I was surprised to discover this. Although technically not a bug since the scheme spec considers this situation unspecified, it makes using multiple-values unreliable. This affects pp as well (pp (values #f #f)) => #<unknown> Arthur

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64 bit gambit
by |/|/ Bendick 21 Sep '08

21 Sep '08

What is the appropriate way of compiling gambit on a 64 bit system? I'm working with gcc 4.0.1 on mac ox 10.5.4 (intel). I tried adding CFLAGS="-m64" to ./configure's command line options which almost worked until the build system attempted to actually create the gsi and gsc. It forgot the -m64 options at that point but manually executing the command with -m64 worked fine. After that though, gsc does not seem to compile scheme files with the the -m64 option which prevents them from being loadable unless i explicitely pass gsc -cc-options "-m64" Is there a way to make gsc remember this or perhaps am I going about the entire thing incorrectly? -- |/|/ Bendick

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bug with write?
by naruto canada 15 Sep '08

15 Sep '08

hi I believe there might be a problem with gambit-c's write function, gambit-c seem to treat the word "syntax" with special meaning, (I'm not entirely sure about this) or that this is a problem with inner defines? I was testing some transformations and ran into this problem: cat z.scm | mzscheme -m -f zzz.scm (define %syntax (lambda (exp cur-env stx-env) (define syntax (lambda (exp cur-env stx-env) (if (eq? stx-env cur-env) (%wrap-syntax exp stx-env 1) (%wrap-syntax (syntax exp (cdr cur-env) stx-env) cur-env 1)))) (%wrap-syntax (syntax exp cur-env stx-env) cur-env -1))) cat z.scm | /usr/gambitc/bin/gsi zzz.scm (define %syntax (lambda (exp cur-env stx-env) (define . #'(lambda (exp cur-env stx-env) (if (eq? stx-env cur-env) (%wrap-syntax exp stx-env 1) (%wrap-syntax (syntax exp (cdr cur-env) stx-env) cur-env 1)))) (%wrap-syntax (syntax exp cur-env stx-env) cur-env -1))) the word "syntax" got translated into ". #'", which is incorrect. # cat z.scm (define (%syntax exp cur-env stx-env) (define (syntax exp cur-env stx-env) (if (eq? stx-env cur-env) (%wrap-syntax exp stx-env 1) (%wrap-syntax (syntax exp (cdr cur-env) stx-env) cur-env 1))) (%wrap-syntax (syntax exp cur-env stx-env) cur-env -1)) # cat zzz.scm (define (pretty-print x)(write x)(newline)) (define trans-define (lambda (l) (if (symbol? (cadr l)) `(define ,(cadr l) ,@(transform (cddr l))) (let ((procname (caadr l)) (formals (cdadr l)) (exps (transform (cddr l)))) `(define ,procname (lambda ,formals ,@exps)))))) (define (transform exp) (cond ((not (pair? exp)) exp) ((and (list? exp) (eq? 'quote (car exp))) exp) ((and (list? exp) (eq? 'define (car exp))) (trans-define exp)) ((list? exp) (map transform exp)) ((pair? exp) (cons (transform (car exp)) (transform (cdr exp)))) (else (begin (pretty-print (list "Which is not entirely unlike tea. " exp))(exit))))) (define (loop) (let ((text (read))) (if (eof-object? text) (exit) (begin (pretty-print (transform text)) (newline) (loop))))) (newline) (loop)

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DrScheme and GambitC
by Nick 14 Sep '08

14 Sep '08

Hello! I believe, every schemer knows about popular IDE DrScheme. It has one nice feature - it allows to choose language level at any time, and this language level vary from very restricted to very rich like MrEd. So I thought I would be great if there was a plugin to DrScheme adding the "Gambit" language level. I searched through web in order to find some pointers how to add custom language level or if people writing their own plugins for DrScheme. But I found not very much :-( If anyone has some info on maybe attempts to add Gambit plugin, or info how to add plugins or anything like this, or finally any advice, relevant or irrelevant :-), please, let me know. With best regards, Nick

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Scribular :: you have to be there
by Bradley Lucier 11 Sep '08

11 Sep '08

For people who look for Scheme apps, see Scribular. It uses PLT Scheme plus LeftParen for the back end, see the blog entry. Brad http://www.scribular.com/

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Re: [gambit-list] DrScheme and GambitC
by William Cook 09 Sep '08

09 Sep '08

Yes, that does count as a breakpoint. However, to me the glass is only 10% full, because I can't select a line of code and "put a breakpoint there". I can only do it on function entry points. So, I would say that Gambit does not have what most people would consider breakpoints. I don't think that more keyboard shortcuts are a replacement for a well-designed user interface. But maybe that's just me. William David St-Hilaire wrote: > William Cook wrote: >> Alex and Joel, >> >> Gambit is reasonable in this respect, although the lack of breakpoints is annoying. > > Hi William! > > I would just like to let you know that gambit has breakpoints, eg: > >> (define (fact n) (if (< n 2) 1 (* (fact (- n 1)) n))) >> (fact 10) > 3628800 >> (break fact) >> (fact 10) > *** STOPPED IN fact, (console)(a)1.23 > 1> ,c > *** STOPPED IN fact, (console)(a)1.23 > 1> ,c > *** STOPPED IN fact, (console)(a)1.23 > 1> ,c > *** STOPPED IN fact, (console)(a)1.23 > 1> ,e > n = 7 > 1> ,c > *** STOPPED IN fact, (console)(a)1.23 > 1> ,e > n = 6 > 1> ,q > >> But I'm tired of typing commands, and I'm tired of copying variable names so that I can execute them. > > using Emacs to debug will have you avoid retyping stuff using word completion, > or alt-p alt-n to browse you previous inputs :) > > David ^_^Y >

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