[MLton-commit] r6585

[Vesa Karvonen]

A couple of clear simplifications using iterator combinators.

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U   mltonlib/trunk/com/ssh/extended-basis/unstable/example/iter/countdown.sml

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Modified: mltonlib/trunk/com/ssh/extended-basis/unstable/example/iter/countdown.sml
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--- mltonlib/trunk/com/ssh/extended-basis/unstable/example/iter/countdown.sml	2008-04-09 08:21:52 UTC (rev 6584)
+++ mltonlib/trunk/com/ssh/extended-basis/unstable/example/iter/countdown.sml	2008-04-09 11:28:55 UTC (rev 6585)
@@ -28,6 +28,8 @@
  * version.
  *)
 
+open Iter.Monad Iter
+
 (*** Expressions ***)
 
 datatype b = ADD | SUB | MUL | DIV
@@ -58,10 +60,10 @@
   | interleave x (y::ys) e =
     (e (x::y::ys) ; interleave x ys (fn ys => e (y::ys)))
 
-fun perms []      e = e [] : unit
-  | perms (x::xs) e = perms xs (fn p => interleave x p e)
+fun perms []      = return []
+  | perms (x::xs) = perms xs >>= interleave x
 
-fun choices xs e = subs xs (fn s => perms s e)
+fun choices xs = subs xs >>= perms
 
 (*** Brute force solution ***)
 
@@ -71,7 +73,7 @@
 
 fun bops e = (e ADD ; e SUB ; e MUL ; e DIV) : unit
 
-fun combine l r e = bops (fn b => e (APP (b, l, r)))
+fun combine l r = map (fn b => APP (b, l, r)) bops
 
 fun exprs []  _ = ()
   | exprs [n] e = e (VAL n)