diff options
| -rw-r--r-- | ccwl/utils.scm | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/ccwl/utils.scm b/ccwl/utils.scm index c20aae1..c75ec91 100644 --- a/ccwl/utils.scm +++ b/ccwl/utils.scm @@ -29,7 +29,10 @@ #:use-module (ice-9 match) #:export (pairify plist->alist - lambda**)) + lambda** + mapn + append-mapn + foldn)) (define (pairify lst) "Return a list of pairs of successive elements of LST." @@ -119,3 +122,37 @@ for example, be invoked as: rest (list #,@(map (compose (cut datum->syntax x <>) symbol->keyword) unary-arguments)))))))))))) + +(define (mapn proc lst) + "Map the procedure PROC over list LST and return a list containing +the results. PROC can return multiple values, in which case, an equal +number of lists are returned." + (apply values + (apply zip + (map (lambda (x) + (call-with-values (cut proc x) list)) + lst)))) + +(define (append-mapn proc lst) + "Map PROC over LST just as in mapn, but append the results +together. PROC can return multiple values, in which case, an equal +number of lists are returned." + (call-with-values (cut mapn proc lst) + (lambda lists + (apply values + (map (lambda (lst) + (apply append lst)) + lists))))) + +(define (foldn proc lst . inits) + "Apply PROC to the elements of LST to build a result, and return +that result. PROC can return multiple values, in which case, an equal +number of values are returned. Each PROC call is (PROC ELEMENT +PREVIOUS ...) where ELEMENT is an element of LST, and (PREVIOUS ...) +is the return from the previous call to PROC or the given INITS for +the first call." + (apply values + (fold (lambda (element results) + (call-with-values (cut apply proc element results) list)) + inits + lst))) |