let strip_string s =
let len = String.length s in
let rec iter_first n =
if n >= len then
None
else
match s.[n] with
' ' | '\t' | '\n' | '\r' -> iter_first (n+1)
| _ -> Some n
in
match iter_first 0 with
None -> ""
| Some first ->
let rec iter_last n =
if n <= first then
None
else
match s.[n] with
' ' | '\t' | '\n' | '\r' -> iter_last (n-1)
| _ -> Some n
in
match iter_last (len-1) with
None -> String.sub s first 1
| Some last -> String.sub s first ((last-first)+1)