diff --git a/src/basis/__string.sml b/src/basis/__string.sml
index 9062231a..abda3453 100644
--- a/src/basis/__string.sml
+++ b/src/basis/__string.sml
@@ -136,6 +136,11 @@ structure String : STRING =
 
     (* basis concat is aka old style implode *)
 
+    fun concatWith _ [] = ""
+      | concatWith _ [s] = s
+      | concatWith sep (s :: ss) =
+	concat (rev (foldl (fn (s, ss) => s :: sep :: ss) [s] ss))
+
     fun compare (x:string,y) = 
       if x<y then LESS else if x>y then GREATER else EQUAL
 
diff --git a/src/basis/string.sml b/src/basis/string.sml
index 45622c48..d2a77af2 100644
--- a/src/basis/string.sml
+++ b/src/basis/string.sml
@@ -81,6 +81,7 @@ signature STRING =
     val sub : (string * int) -> char
     val extract : (string * int * int option) -> string 
     val concat    : string list -> string
+    val concatWith : string -> string list -> string
     val ^         : string * string -> string
     val implode   : char list -> string
     val explode : string -> char list