OCaml 入門。Python の str.swapcase() みたいな。

swapcase.ml

let swapcase c = match c with
  | 'A' .. 'Z' -> Char.lowercase c
  | 'a' .. 'z' -> Char.uppercase c
  | _ -> c
 
let swapcase_s s = String.map swapcase s;;

swapcase_s "AbC";; (* => "aBc" *)