Re: comparator in match pattern

[Vivien Kraus <vivien@planete-kraus.eu>]

Le mercredi 28 juin 2023 à 15:38 +0200, Damien Mattei a écrit :
> scheme@(guile-user)> (use-modules (ice-9 match))
> scheme@(guile-user)> (match (list 1 /) ((list c (cut equal? <> /))

So, you want to match against the / symbol, not the value of a variable
named /?

The simplest case would be to use quasiquote/unquote syntax in the
pattern:

(match (list 1 '/) 
  (`(,c /) 
   c))

should give: 1, the value of c

If you don’t understand quasiquote/unquote, you can use the slightly
uglier:

(match (list 1 '/) 
  ((c '/) 
   c))

If / is the name of a variable (why not), you can do:

(use-modules (srfi srfi-26))
(let ((/ 42)) 
  (match (list 1 42) 
    ((c (? (cut equal? <> /))) 
     c)))

In any case, no need to write "list" in the pattern.

Vivien