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| author | Hugo Hörnquist <hugo@lysator.liu.se> | 2020-07-20 03:22:50 +0200 |
|---|---|---|
| committer | Hugo Hörnquist <hugo@lysator.liu.se> | 2020-07-20 04:19:03 +0200 |
| commit | 91f33fc900e96083aaaf41d1b41d2cd0ada1aa22 (patch) | |
| tree | 18f7d0c5a3cff65caad8f002996ab29fd18c168a | |
| parent | Remove invalid export tree-map from (util). (diff) | |
| download | calp-91f33fc900e96083aaaf41d1b41d2cd0ada1aa22.tar.gz calp-91f33fc900e96083aaaf41d1b41d2cd0ada1aa22.tar.xz | |
Add split-by.
| -rw-r--r-- | module/util.scm | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/module/util.scm b/module/util.scm index f09cc315..76877d10 100644 --- a/module/util.scm +++ b/module/util.scm @@ -406,6 +406,24 @@ (hash-set! h key (cons value (hash-ref h key '()))))) (hash-map->list list h))) +;; (group-by '(0 1 2 3 4 2 5 6) 2) +;; ⇒ ((0 1) (3 4) (5 6)) +(define-public (split-by list item) + (let loop ((done '()) + (current '()) + (rem list)) + (cond [(null? rem) + (reverse (cons (reverse current) done))] + [(eqv? item (car rem)) + (loop (cons (reverse current) done) + '() + (cdr rem))] + [else + (loop done + (cons (car rem) current) + (cdr rem))]))) + + ;; Returns the cross product between l1 and l2. ;; each element is a cons cell. (define (cross-product% l1 l2) |