MODULE MutualRecursion;

  IMPORT Out;

  TYPE
    Fn = PROCEDURE(n:INTEGER):INTEGER;

  PROCEDURE^ M(n:INTEGER):INTEGER;

  PROCEDURE F(n:INTEGER):INTEGER;
  BEGIN
    IF n=0 THEN RETURN 1
    ELSE RETURN n-M(F(n-1))
    END;
  END F;

  PROCEDURE M(n:INTEGER):INTEGER;
  BEGIN
    IF n=0 THEN RETURN 0
    ELSE RETURN n-F(M(n-1))
    END;
  END M;

(* Print the first few values of one of the functions *)
  PROCEDURE Show(name:ARRAY OF CHAR;fn:Fn);
    CONST Max = 15;
    VAR i:INTEGER;
  BEGIN
    Out.String(name);
    Out.String(": ");
    FOR i := 0 TO Max DO
      Out.Int(fn(i),0);
      Out.String(" ");
    END;
    Out.Ln;
  END Show;

(* Show the first values of both F and M *)
BEGIN
  Show("F", F);
  Show("M", M);
END MutualRecursion.