Add belt_String as a set of string utils

jscomp/others/.depend

@@ -85,6 +85,7 @@ belt_SetString.cmj : belt_internalSetString.cmj belt_internalAVLset.cmj \
     belt_Array.cmj belt_SetString.cmi
 belt_MutableStack.cmj : belt_MutableStack.cmi
 belt_MutableQueue.cmj : belt_Array.cmj belt_MutableQueue.cmi
+belt_String.cmj : belt_String.cmi
 node_child_process.cmj : node.cmj
 js_math.cmj :
 js_dict.cmj : js_array.cmj js_dict.cmi
@@ -145,6 +146,7 @@ belt_SetInt.cmi :
 belt_SetString.cmi :
 belt_MutableStack.cmi :
 belt_MutableQueue.cmi :
+belt_String.cmi :
 js_dict.cmi :
 js_cast.cmi :
 dom.cmi : dom_storage.cmi

jscomp/others/Makefile

@@ -50,6 +50,7 @@ SOURCE_LIST= node_path node_fs node_process dict node_module js_array js_string
 	belt_SetString\
 	belt_MutableStack\
 	belt_MutableQueue\
+	belt_String\
 	node_child_process \
 	js_math\
 	js_dict js_date js_global js_cast js_promise\

jscomp/others/belt.ml

@@ -255,3 +255,10 @@ module Result = Belt_Result
     Utilities for set up debugging
 *)
 module Debug = Belt_Debug
+
+(** {!Belt.String}
+
+    String utilities
+*)
+module String = Belt_String
+

jscomp/others/belt_String.ml

@@ -0,0 +1,12 @@
+open String
+
+let split_on_char sep s =
+  let r = ref [] in
+  let j = ref (length s) in
+  for i = length s - 1 downto 0 do
+    if unsafe_get s i = sep then begin
+      r := sub s (i + 1) (!j - i - 1) :: !r;
+      j := i
+    end
+  done;
+  sub s 0 !j :: !r

jscomp/others/belt_String.mli

@@ -0,0 +1 @@
+val split_on_char : char -> string -> string list