How do I strip whitespace from a string in OCaml?

Question

To learn the basics of OCaml, I'm solving one of the easy facebook engineering puzzles using it. Essentially, I'd like to do something like the following Python code:

some_str = some_str.strip()

That is, I'd like to strip all of the whitespace from the beginning and the end. I don't see anything obvious to do this in the OCaml Str library. Is there any easy way to do this, or am I going to have to write some code to do it (which I wouldn't mind, but would prefer not to :) ).

Bear in mind that I'm limited to what's in the libraries that come with the OCaml distribution.

Answer 1

how about

let trim str =   if str = "" then "" else   let search_pos init p next =
    let rec search i =
      if p i then raise(Failure "empty") else
      match str.[i] with
      | ' ' | '\n' | '\r' | '\t' -> search (next i)
      | _ -> i
    in
    search init   in   let len = String.length str in   try
    let left = search_pos 0 (fun i -> i >= len) (succ)
    and right = search_pos (len - 1) (fun i -> i < 0) (pred)
    in
    String.sub str left (right - left + 1)   with   | Failure "empty" -> "" ;;

(Via Code Codex)

Answer 2

It is really a mistake to limit yourself to the standard library, since the standard ilbrary is missing a lot of things. If, for example, you were to use Core, you could simply do:

open Core.Std

let x = String.strip "  foobar   "
let () = assert (x = "foobar")

You can of course look at the sources of Core if you want to see the implementation. There is a similar function in ExtLib.