the same expression in Scheme would be:
(set! xp (/ (- x (* v t)) (sqrt (- 1 (/ (expt v 2) (expt c 2))))))
> xp
-1102228130.2405226
a bit less readable than:
{xp <- {x - v * t} / (sqrt {1 - v ** 2 / c ** 2})}
-1102228130.2405226
or:
{xp ← {x - v * t} / (sqrt {1 - v ** 2 / c ** 2})}
-1102228130.2405226
note: i admit the ← is hard to get on keyboards ;-)
On Sat, Apr 15, 2023 at 6:15 PM Damien Mattei <damien.mat...@gmail.com>
wrote:
> it works pretty well again now the new version is debugged, this code is
> related to infix evaluation in Scheme+ with operator precedence , here is
> an example:
>
> ;;; compiled
> /Users/mattei/.cache/guile/ccache/3.0-LE-8-4.6/usr/local/share/guile/site/3.0/Scheme+.scm.go
> scheme@(guile-user)> { 4 + 3 * 2 - 19 < 0 - 4}
> $1 = #t
> scheme@(guile-user)> (define i 3)
> scheme@(guile-user)> {i <- i + 1}
> $2 = 4
> scheme@(guile-user)> (define c 300000)
> scheme@(guile-user)> (define v 299990)
> scheme@(guile-user)> (define t 30)
> scheme@(guile-user)> (define x 120)
> scheme@(guile-user)> (declare xp)
> scheme@(guile-user)> {xp <- {x - v * t} / (sqrt {1 - v ** 2 / c ** 2})}
> $3 = -1102228130.2405226
> scheme@(guile-user)> '{xp <- {x - v * t} / (sqrt {1 - v ** 2 / c ** 2})}
> $4 = ($nfx$ xp <- ($nfx$ x - v * t) / (sqrt ($nfx$ 1 - v ** 2 / c ** 2)))
>
> could be written also this way:
> {c <+ 300000}
> {v <+ 299990}
> {t <+ 30}
> {x <+ 120}
> (declare xp)
> { xp <- {x - v * t} / (sqrt {1 - v ** 2 / c ** 2}) }
> = -1102228130.2405226
> xp
> = -1102228130.2405226
>
> it is not far from what the Python syntax allow in term of readability:
>
> c=300000
> v=299990
> t=30
> x=120
> xp = (x - v * t) / math.sqrt (1 - v ** 2 / c ** 2)
> xp
> -1102228130.2404253
>
>
> On Sat, Apr 15, 2023 at 4:45 PM Damien Mattei <damien.mat...@gmail.com>
> wrote:
>
>> my problem is solved by quoting the variable that CAN store a special
>> form (example: <-) and forcing its evaluation ! : (eval (quote opspecial)
>> (interaction-environment))
>>
>> here is my 'else clause:
>>
>> (else (! ident (eval (quote opspecial) (current-namespace)) term1 op
>> term2))))))
>>
>> for Racket, in Guile , not tested but it should be:
>> (else (! ident (eval (quote opspecial) (interaction-environment)) term1
>> op term2))))))
>>
>> again the else clause WILL NEVER be evaluated with opspecial being a
>> special form but it is always expanded and that was enought to make an
>> error.
>>
>> I admit reading Kent Dybvig article on macro and with a good scheme (as
>> Guile) that implement some special feature of the article and it should
>> exist a more elegant solution than : (eval (quote opspecial)
>> (interaction-environment))
>> quoting with immediate evaluation ! :-/
>> Damien
>>
>>
>>
>> On Sat, Apr 15, 2023 at 4:18 PM Damien Mattei <damien.mat...@gmail.com>
>> wrote:
>>
>>> yes i tried it, i often get this answer :-) with this sort of problem i
>>> recurrent have with macros and it never helps ,at the point i never
>>> understood what is the use of this option in syntax-rules.
>>>
>>> My error i think was to forget the expansion stage of macro expansion
>>> that is always done for all the macros used in an expression at any level,
>>> even if the code is not used in a branch of 'if ,'cond or other conditional
>>> the macros will be expansed.
>>>
>>> I will quote the <- in the opspecial and tried to eval it later, the
>>> problem is with eval which is not really normalised between all
>>> implementations of scheme concerning its environment of evaluation.
>>> I will post the result.
>>> The problem was also that in an infix evaluator i wanted to be able to
>>> evaluate all procedure (that is ok) and all the macro too which is not
>>> always possible with the evaluation technique i use ,it is hard to write an
>>> infix evaluator with precedence in the language itself.But the problem
>>> arise only with the special forms, so first i quoted them all but then i
>>> can not find the difference in the language with '(sin 30) a procedure call
>>> and '(1 2 3) a list when evealuating it is has sense for (sin 30) but not
>>> for (1 2 3) then i removed all quotation and the macro problem arise...
>>> just after i added some overloading functionalities in my Scheme+ when
>>> using abstract types the evaluation of abstract object (list) with for
>>> example the + operator overloaded became a problem.
>>> Damien
>>>
>>> On Sat, Apr 15, 2023 at 3:50 PM Matt Wette <matt.we...@gmail.com> wrote:
>>>
>>>> Did you try using the following?
>>>>
>>>> (define-syntax $nfx$
>>>> (syntax-rules (<-)
>>>> ((...
>>>>
>>>>
>>>> On 4/14/23 4:02 AM, Damien Mattei wrote:
>>>> > hello,
>>>> >
>>>> > i have 2 macros used in one expression like this:
>>>> > scheme@(guile-user)> (define i 2)
>>>> > scheme@(guile-user)> {i <- i + 1}
>>>> > and i got this error:
>>>> > While compiling expression:
>>>> > Syntax error:
>>>> > unknown location: source expression failed to match any pattern in
>>>> form <-
>>>> >
>>>> > i use SRFI-105 so :
>>>> > '{i <- i + 1} expand in:
>>>> > ($nfx$ i <- i + 1)
>>>> >
>>>> > and i'm expecting $nfx$ to be called but none of this happens:
>>>> > scheme@(guile-user)> ($nfx$ i <- i + 1)
>>>> > While compiling expression:
>>>> > Syntax error:
>>>> > unknown location: source expression failed to match any pattern in
>>>> form <-
>>>> >
>>>> > it seems to be the <- macro and i do not understand why?
>>>> >
>>>> > any idea?
>>>> >
>>>> > macros are defined like this for the beginning:
>>>> > ;; from file assignment.scm
>>>> > (define-syntax <-
>>>> >
>>>> > (syntax-rules ()
>>>> > ;; special form like : (<- ($bracket-apply$ T 3)
>>>> ($bracket-apply$ T 4))
>>>> >
>>>> > ;; one dimension array, example: {a[4] <- 7}
>>>> > ;; $bracket-apply$ is from SRFI 105 bracket-apply is an
>>>> argument of
>>>> > the macro
>>>> > ((_ (bracket-apply container index) expr)
>>>> >
>>>> > ....
>>>> >
>>>> > ;; from file scheme-infix.scm
>>>> > (define-syntax $nfx$
>>>> > (syntax-rules ()
>>>> >
>>>> > ((_ ident opspecial term1 op term2) (cond ((or (equal? (quote
>>>> > opspecial) (quote <-)) (equal? (quote opspecial) (quote ←)))
>>>> > (begin
>>>> > (display "$nfx$") (newline)
>>>> > (opspecial ident (op term1 term2)))) ;; {ident <- {term1 op term2}}
>>>> >
>>>> > ...
>>>> >
>>>> >
>>>> > it is in a module like this:
>>>> >
>>>> > (define-module (Scheme+)
>>>> >
>>>> > #:use-module (growable-vector)
>>>> > #:use-module (srfi srfi-69) ;; Basic hash tables
>>>> > #:use-module (srfi srfi-31) ;; rec
>>>> > #:export ($nfx$ def $bracket-apply$ <- ← -> → <+ ⥆ +> ⥅ declare $
>>>> & condx
>>>> > <> ≠ ** <v v> ⇜ ⇝ repeat)
>>>> > #:replace (do when unless))
>>>> >
>>>> >
>>>> >
>>>> > (include-from-path "def.scm")
>>>> > (include-from-path "array.scm")
>>>> > (include-from-path "set-values-plus.scm")
>>>> > (include-from-path "apply-square-brackets.scm")
>>>> > (include-from-path "assignment.scm")
>>>> > (include-from-path "declare.scm")
>>>> > (include-from-path "condx.scm")
>>>> > (include-from-path "block.scm")
>>>> > (include-from-path "not-equal.scm")
>>>> > (include-from-path "exponential.scm")
>>>> > (include-from-path "while-do-when-unless.scm")
>>>> > (include-from-path "repeat-until.scm")
>>>> > (include-from-path "scheme-infix.scm")
>>>> >
>>>> > if it can help.
>>>> >
>>>> > Regards,
>>>> > Damien
>>>>
>>>
