add CCString.Split.{left,right}_exn

src/core/CCString.cppo.ml

@@ -199,15 +199,19 @@ module Split = struct
   let seq ~by s = _mkseq ~by s _tuple3
   let seq_cpy ~by s = _mkseq ~by s String.sub
 
-  let left ~by s =
+  let left_exn ~by s =
     let i = find ~sub:by s in
-    if i = ~-1 then None
+    if i = ~-1 then raise Not_found
-    else Some (String.sub s 0 i, String.sub s (i+1) (String.length s - i - 1))
+    else String.sub s 0 i, String.sub s (i+1) (String.length s - i - 1)
 
-  let right ~by s =
+  let left ~by s = try Some (left_exn ~by s) with Not_found -> None
+
+  let right_exn ~by s =
     let i = rfind ~sub:by s in
-    if i = ~-1 then None
+    if i = ~-1 then raise Not_found
-    else Some (String.sub s 0 i, String.sub s (i+1) (String.length s - i - 1))
+    else String.sub s 0 i, String.sub s (i+1) (String.length s - i - 1)
+
+  let right ~by s = try Some (right_exn ~by s) with Not_found -> None
 end
 
 let compare_versions a b =

src/core/CCString.mli

@@ -299,6 +299,11 @@ module Split : sig
       the string
       @since 0.12 *)
 
+  val left_exn : by:string -> string -> string * string
+  (** Split on the first occurrence of [by] from the leftmost part of the string
+      @raise Not_found if [by] is not part of the string
+      @since NEXT_RELEASE *)
+
   (*$T
     Split.left ~by:" " "ab cde f g " = Some ("ab", "cde f g ")
     Split.left ~by:"_" "abcde" = None
@@ -309,6 +314,11 @@ module Split : sig
       the string
       @since 0.12 *)
 
+  val right_exn : by:string -> string -> string * string
+  (** Split on the first occurrence of [by] from the rightmost part of the string
+      @raise Not_found if [by] is not part of the string
+      @since NEXT_RELEASE *)
+
   (*$T
     Split.right ~by:" " "ab cde f g" = Some ("ab cde f", "g")
     Split.right ~by:"_" "abcde" = None