mlton/atoms/field.fun

   1 (* Copyright (C) 1999-2006 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  * Copyright (C) 1997-2000 NEC Research Institute.
   4  *
   5  * MLton is released under a BSD-style license.
   6  * See the file MLton-LICENSE for details.
   7  *)
   8
   9 functor Field (S: FIELD_STRUCTS): FIELD =
  10 struct
  11
  12 open S
  13
  14 datatype t =
  15    Int of int
  16  | Symbol of Symbol.t
  17
  18 val equals =
  19    fn (Int n, Int n') => Int.equals (n, n')
  20     | (Symbol s, Symbol s') => Symbol.equals (s, s')
  21     | _ => false
  22
  23 val toString =
  24    fn Int n => Int.toString (n + 1)
  25     | Symbol s => Symbol.toString s
  26
  27 val layout = Layout.str o toString
  28
  29 val op <= =
  30    fn (Int n, Int n') => Int.<= (n, n')
  31     | (Symbol s, Symbol s') => Symbol.<= (s, s')
  32     | (Symbol _, Int _) => false
  33     | (Int _, Symbol _) => true
  34
  35 end