Re: cond(itionals) with optional execution of statements

[Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>]

Hello Damien!

I am not sure I understand the reasoning behind condx: I think cond is already a
macro, which only evaluates a consequent, if the predicate of its case is #t.
Additionally multiple expressions are possible in each branch.

To clarify, I ask: What is the case, where condx does or does not evaluate some
code, when cond would not or would? Or is it rather about the different nesting
/ sequence of expressions, which condx seems to enable? I think the flow you
demonstrate might save a bit of nesting.

Best regards,
Zelphir

On 9/11/21 11:14 AM, Damien Mattei wrote:
> hello,
>
> i wrote a little macro (file condx.scm)  that allow :  cond(itionals) with
> optional execution of statements before:
>
> (define-syntax condx
>   (syntax-rules (exec)
>     ((_)
>      (error 'condx "No else clause"))
>     ((_ (else e ...))
>      (let () e ...))
>     ((_ (exec s ...) d1 ...)
>      (let () s ... (condx d1 ...)))
>     ((_ (t e ...) tail ...)
>      (if t
>          (let () e ...)
>          (condx tail ...)))))
>
> use it like that:
>
> mattei@macbook-pro-touch-bar library-FunctProg % guile
> GNU Guile 3.0.7
> Copyright (C) 1995-2021 Free Software Foundation, Inc.
>
> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> This program is free software, and you are welcome to redistribute it
> under certain conditions; type `,show c' for details.
>
> Enter `,help' for help.
> scheme@(guile-user)> (load "condx.scm")
> ;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
> ;;;       or pass the --no-auto-compile argument to disable.
> ;;; compiling /Users/mattei/Dropbox/git/library-FunctProg/condx.scm
> ;;; compiled
> /Users/mattei/.cache/guile/ccache/3.0-LE-8-4.5/Users/mattei/Dropbox/git/library-FunctProg/condx.scm.go
> scheme@(guile-user)> (define x 1)
>
> (condx ((= x 7) 'never)
>         (exec
>           (define y 3)
>           (set! x 7))
>         ((= y 1) 'definitely_not)
>         (exec
>           (set! y 10)
>           (define z 2))
>         ((= x 7) (+ x y z))
>         (else 'you_should_not_be_here))
> $1 = 19
>
> i share it to have idea about critics or idea to improve it as it will be
> part of  a Scheme extension to scheme language that will include other
> features....
>
> have a good day
>
> Damien

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repositories: https://notabug.org/ZelphirKaltstahl