lib/mlton/basic/char-pred.sml

   1 (* Copyright (C) 1999-2006 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  *
   4  * MLton is released under a BSD-style license.
   5  * See the file MLton-LICENSE for details.
   6  *)
   7
   8 fun contains s =
   9          let
  10             val a = Array.array(numChars, false)
  11             val n = String.size s
  12             fun loop i =
  13                if i >= n then ()
  14                else (Array.update(a, ord(String.sub(s, i)), true)
  15                      ; loop(i + 1))
  16          in loop 0
  17             ; fn c => Array.sub(a, ord c)
  18          end
  19
  20       fun notContains s = not o (contains s)
  21
  22       fun memoize (f: char -> 'a): char -> 'a =
  23          let val a = Array.tabulate(numChars, f o chr)
  24          in fn c => Array.sub(a, ord c)
  25          end
  26
  27       local
  28          val not = fn f => memoize(not o f)
  29          infix or andd
  30          fun f or g = memoize(fn c => f c orelse g c)
  31          fun f andd g = memoize(fn c => f c andalso g c)