[bug#68271] [PATCH 1/3] guix: utils: Add delete-duplicates/sort.

[Ludovic Courtès]

Christopher Baines <mail@cbaines.net> skribis:

> Similar to delete-duplicates, but sorts the list first and then compares the
> pairs in the list. This is faster than delete-duplicates for larger lists.

We’re dealing with small lists here though (derivation inputs).  Did you
try to time the benefit?

There’s a complexity/benefit tradeoff and I wonder if it cuts it.

> +(define* (delete-duplicates/sort unsorted-lst less #:optional (equal? eq?))
> +  (if (null? unsorted-lst)
> +      unsorted-lst

This ‘if’ is unnecessary.

> +      (let ((sorted-lst (sort unsorted-lst
> +                              ;; Sort in the reverse order
> +                              (lambda (a b) (eq? #f (less a b))))))

Just: (negate less).

> +        (let loop ((lst (cdr sorted-lst))
> +                   (last-element (car sorted-lst))
> +                   (result (list (car sorted-lst))))
> +          (if (null? lst)
> +              result
> +              (let ((current-element (car lst)))

Please follow the convention of using ‘match’ rather than car caddr
caddddar (info "(guix) Data Types and Pattern Matching"):

  (match lst
    (()
     result)
    ((head . tail)
     …))

Ludo’.