--- a/src/Pure/library.ML Sat Jan 26 17:08:38 2008 +0100
+++ b/src/Pure/library.ML Sat Jan 26 17:08:39 2008 +0100
@@ -110,6 +110,7 @@
val map_split: ('a -> 'b * 'c) -> 'a list -> 'b list * 'c list
val split_list: ('a * 'b) list -> 'a list * 'b list
val separate: 'a -> 'a list -> 'a list
+ val surround: 'a -> 'a list -> 'a list
val replicate: int -> 'a -> 'a list
val is_prefix: ('a * 'a -> bool) -> 'a list -> 'a list -> bool
val take_prefix: ('a -> bool) -> 'a list -> 'a list * 'a list
@@ -535,6 +536,9 @@
fun separate s (x :: (xs as _ :: _)) = x :: s :: separate s xs
| separate _ xs = xs;
+fun surround s (x :: xs) = s :: x :: surround s xs
+ | surround s [] = [s];
+
(*make the list [x, x, ..., x] of length n*)
fun replicate (n: int) x =
let fun rep (0, xs) = xs