(*
  vim: syntax=sml

  A structure for treating books as ORDERED types.

  $Id: Book.sml,v 1.1 2004/09/09 21:15:11 cstork Exp $

  Copyright (c) 2003-2004 by Peter H. Froehlich <phf@acm.org>.
  All rights reserved.

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of
  the License, or (at your option) any later version.
*)

structure Book: ORDERED =
  struct
    type t = {
      author: string,
      title: string,
      year: int,
      isbn: string
    };
    fun compare {author=ax, title=tx, year=yx, isbn=ix}
                {author=ay, title=ty, year=yy, isbn=iy} =
      if ax < ay then LESS
      else if ax > ay then GREATER
      else
        if tx < ty then LESS
        else if tx > ty then GREATER
        else
          if yx < yy then LESS
          else if yx > yy then GREATER
          else
            if ix < iy then LESS
            else if ix > iy then GREATER
            else EQUAL;
  end;