# HG changeset patch
# User haftmann
# Date 1124954620 -7200
# Node ID 4b0dc89de43bd69b6890d6fa9d99c3c28e7ca42e
# Parent  5be3a21ec949d46c8040d2038c5afff706393420
added ? combinator for conditional transformations

diff -r 5be3a21ec949 -r 4b0dc89de43b src/Pure/library.ML
--- a/src/Pure/library.ML	Thu Aug 25 09:23:13 2005 +0200
+++ b/src/Pure/library.ML	Thu Aug 25 09:23:40 2005 +0200
@@ -13,6 +13,8 @@
   union_string inter inter_int inter_string subset subset_int
   subset_string;
 
+infix 2 ?;
+
 infix 3 oo ooo oooo;
 
 signature BASIC_LIBRARY =
@@ -30,6 +32,7 @@
   val |>>> : ('a * 'c) * ('a -> 'b * 'd) -> 'b * ('c * 'd)
   val #> : ('a -> 'b) * ('b -> 'c) -> 'a -> 'c
   val #-> : ('a -> 'c * 'b) * ('c -> 'b -> 'd) -> 'a -> 'd
+  val ? : ('a -> bool) * ('a -> 'a) -> 'a -> 'a
   val ` : ('b -> 'a) -> 'b -> 'a * 'b
   val tap: ('b -> 'a) -> 'b -> 'b
   val oo: ('a -> 'b) * ('c -> 'd -> 'a) -> 'c -> 'd -> 'b
@@ -320,6 +323,9 @@
 fun f #> g = g o f;
 fun f #-> g = uncurry g o f;
 
+(*conditional application*)
+fun b ? f = fn x => if b x then f x else x
+
 (*view results*)
 fun `f = fn x => (f x, x);
 fun tap f x = (f x; x);