monads: Add mmap.

* ravanan/work/monads.scm (mmap): New function.
(state-map): New public function.

1 files changed, 9 insertions, 0 deletions

diff --git a/ravanan/work/monads.scm b/ravanan/work/monads.scm
index 830e7ce..a5aea5f 100644
--- a/ravanan/work/monads.scm
+++ b/ravanan/work/monads.scm
@@ -40,6 +40,7 @@
             state-let*
             state-begin
             state-sequence
+            state-mmap
             current-state
             set-current-state
             run-with-state))
@@ -85,6 +86,11 @@ of values."
                               mvalues)))
       (return (reverse reverse-list)))))
 
+(define (mmap monad-type mproc . lists)
+  "Map monadic funcion @var{mproc} in @var{monad-type} over @var{lists} and return
+a monadic list."
+  (sequence monad-type (apply map mproc lists)))
+
 (define-immutable-record-type <maybe>
   (maybe value valid?)
   maybe?
@@ -243,6 +249,9 @@ maybe-monadic."
 (define state-sequence
   (cut sequence %state-monad <>))
 
+(define state-map
+  (cut mmap %state-monad <> <...>))
+
 (define (current-state)
   "Return the current state as a state-monadic value."
   (lambda (state)