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## Re: cond(itionals) with optional execution of statements

 From: Damien Mattei Subject: Re: cond(itionals) with optional execution of statements Date: Sun, 12 Sep 2021 19:05:18 +0200

```Hello Zelphir,

condx evaluate all code(s) in the 'exec' block until a conditional is true,
it then evaluate the consequent code of course.
So ,yes your true it saves a lot of nesting parenthesis as in this example:

here a code with condx and without it:

(define (ssigma-proto-condx L t)

(set! cpt {cpt + 1})

(define ls (length L))
(define dyn (array-ref dyna ls t))

;; dyna[ls][t] means 0: unknown solution, 1: solution found, 2: no solution

(condx [(not (zero? dyn)) (one? dyn)]
[(null? L) (array-set! dyna 2 ls t) #f] ;; return #f

[exec (define c (first L))]

;; c is the solution
[{c = t} (array-set! dyna 1 ls t) #t]  ;; return #t

[exec (define R (rest L))]

;; continue searching a solution in the rest
[{c > t} (define s (ssigma-proto R t))
(array-set! dyna
(one-two s)
ls t)
s] ;; return s

;; else :
;; c < t at this point
;; c is part of the solution or his approximation
;; or c is not part of solution
[else (define s {(ssigma-proto R {t - c}) or (ssigma-proto R t)})
(array-set! dyna (one-two s)
ls t)
s]))

without condx:

(define (ssigma-proto L t)

(set! cpt {cpt + 1})

(define ls (length L))
(define dyn (array-ref dyna ls t))

;; dyna[ls][t] means 0: unknown solution, 1: solution found, 2: no solution

(cond [(not (zero? dyn)) (one? dyn)]
[(null? L) (array-set! dyna 2 ls t) #f] ;; return #f

[else (let [(c (first L))]

(if {c = t} ;; c is the solution

(begin
(array-set! dyna 1 ls t)
#t)  ;; return #t

;; else
(let [(R (rest L))]

(if {c > t}   ;; continue searching a solution in the rest

(let [(s (ssigma-proto R t))]
(array-set! dyna
(one-two s)
ls t)

s) ;; return s

;; else
;; c < t at this point
;; c is part of the solution or his approximation
;; or c is not part of solution
(let [(s {(ssigma-proto R {t - c}) or (ssigma-proto R
t)})]
(array-set! dyna (one-two s)
ls t)
s)))))
] ))

there a lot more of indentation and nesting.

Note also that the use of let () in condx definition allow to use define in
consequent and 'exec' block.

Damien

On Sun, Sep 12, 2021 at 11:41 AM Zelphir Kaltstahl <
zelphirkaltstahl@posteo.de> wrote:

> Hello Damien!
>
> I am not sure I understand the reasoning behind condx: I think cond is
> 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.
> > ;;; 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
>
> --
> repositories: https://notabug.org/ZelphirKaltstahl
>
>

```