diff options
Diffstat (limited to 'guix/utils.scm')
| -rw-r--r-- | guix/utils.scm | 29 |
1 files changed, 28 insertions, 1 deletions
diff --git a/guix/utils.scm b/guix/utils.scm index d7c37e37d1..f13e585e2b 100644 --- a/guix/utils.scm +++ b/guix/utils.scm @@ -59,7 +59,8 @@ %current-system version-compare version>? - package-name->name+version)) + package-name->name+version + fold2)) ;;; @@ -463,6 +464,32 @@ introduce the version part." ((head tail ...) (loop tail (cons head prefix)))))) +(define fold2 + (case-lambda + ((proc seed1 seed2 lst) + "Like `fold', but with a single list and two seeds." + (let loop ((result1 seed1) + (result2 seed2) + (lst lst)) + (if (null? lst) + (values result1 result2) + (call-with-values + (lambda () (proc (car lst) result1 result2)) + (lambda (result1 result2) + (loop result1 result2 (cdr lst))))))) + ((proc seed1 seed2 lst1 lst2) + "Like `fold', but with a two lists and two seeds." + (let loop ((result1 seed1) + (result2 seed2) + (lst1 lst1) + (lst2 lst2)) + (if (or (null? lst1) (null? lst2)) + (values result1 result2) + (call-with-values + (lambda () (proc (car lst1) (car lst2) result1 result2)) + (lambda (result1 result2) + (fold2 proc result1 result2 (cdr lst1) (cdr lst2))))))))) + ;;; ;;; Source location. |