DEFINITION MODULE Rationals;

	(********************************************************)
	(*							*)
	(*		Arithmetic on rational numbers		*)
	(*							*)
	(*  Programmer:		P. Moylan			*)
	(*  Last edited:	2 May 1994			*)
	(*  Status:		OK				*)
	(*							*)
	(********************************************************)

TYPE Rational = RECORD
		    num: INTEGER;
		    denom: CARDINAL;
		END (*RECORD*);

PROCEDURE Zero (): Rational;

    (* Returns a representation of zero. *)

PROCEDURE Unity (): Rational;

    (* Returns a representation of the number 1. *)

PROCEDURE Add (x, y: Rational): Rational;

    (* Returns x+y. *)

PROCEDURE Subtract (x, y: Rational): Rational;

    (* Returns x-y. *)

PROCEDURE Multiply (x, y: Rational): Rational;

    (* Returns x*y. *)

PROCEDURE Divide (x, y: Rational): Rational;

    (* Returns x/y. *)

PROCEDURE Reciprocal (x: Rational): Rational;

    (* Returns 1/x. *)

PROCEDURE Compare (x, y: Rational): INTEGER;

    (* Returns 0 if x=y, <0 if x<y, and >0 if x>y. *)

END Rationals.