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-rw-r--r--guix/monads.scm16
1 files changed, 9 insertions, 7 deletions
diff --git a/guix/monads.scm b/guix/monads.scm
index ec2b7f8b3b..c2c6f1a03d 100644
--- a/guix/monads.scm
+++ b/guix/monads.scm
@@ -209,13 +209,15 @@ monadic value seeded by INIT."
(define (mapm monad mproc lst)
"Map MPROC over LST, a list of monadic values in MONAD, and return a monadic
-list."
- (foldm monad
- (lambda (item result)
- (mlet monad ((item (mproc item)))
- (return (cons item result))))
- '()
- (reverse lst)))
+list. LST items are bound from left to right, so effects in MONAD are known
+to happen in that order."
+ (mlet monad ((result (foldm monad
+ (lambda (item result)
+ (mlet monad ((item (mproc item)))
+ (return (cons item result))))
+ '()
+ lst)))
+ (return (reverse result))))
(define-inlinable (sequence monad lst)
"Turn the list of monadic values LST into a monadic list of values, by