new modules and neatened exposure of official stdlib code

lib/string.ml

@@ -1,11 +1,49 @@
 open General
 
-let ( + ) = FromStdlib.string_concat
 
-let length = FromStdlib.string_length
+external bytes_create : int -> bytes = "caml_create_bytes"
+external string_blit : string -> int -> bytes -> int -> int -> unit = "caml_blit_string" [@@noalloc]
+external bytes_blit : bytes -> int -> bytes -> int -> int -> unit = "caml_blit_bytes" [@@noalloc]
+external bytes_unsafe_to_string : bytes -> string = "%bytes_to_string"
+external format_int : string -> int -> string = "caml_format_int"
+external format_float : string -> float -> string = "caml_format_float"
 
-let of_int = FromStdlib.string_of_int
 
-let of_float = FromStdlib.string_of_float
+external length : string -> int = "%string_length"
 
-let of_bool = FromStdlib.string_of_bool
+let of_int n =
+    format_int "%d" n
+
+let of_bool bool =
+    if bool then
+        "true"
+    else
+        "false"
+
+let ( + ) s1 s2 =
+    let l1 = length s1 in
+    let l2 = length s2 in
+
+    let s = bytes_create Int.(l1 + l2) in
+
+    string_blit s1 0 s 0 l1;
+    string_blit s2 0 s l1 l2;
+
+    bytes_unsafe_to_string s
+
+
+external string_get : string -> int -> char = "%string_safe_get"
+let valid_float_lexem s =
+    let l = length s in
+    let rec loop i =
+        if i >= l then s + "." else
+        match string_get s i with
+        | '0' .. '9' | '-' -> loop Int.(i + 1)
+        | _ -> s
+    in
+    
+    loop 0
+
+
+let of_float f =
+    valid_float_lexem (format_float "%.12g" f)