(* lin-ord.sig *)

(* Copyright (C) 2006 Alley Stoughton

   This file is part of crypto, a cryptogram encoder/decoder.  See the
   file COPYING.txt for copying and usage restrictions *)

(* a type together with a linear ordering on that type *)

signature LIN_ORD =
sig

type elem

(* compare(x, y) always terminates, has no side-effects, and
   always evaluates to the same value (two values are the SAME,
   or are EQUAL, iff there is no way of telling them apart)

   compare(x, y) = EQUAL iff x and y are equal

   compare(x, y) = LESS iff compare(y, x) = GREATER

   if compare(x, y) = LESS and compare(y, z) = LESS,
   then compare(x, z) = LESS *)

val compare : elem * elem -> order

end;