MODULE MutualRecursion;
FROM InOut IMPORT WriteCard, WriteString, WriteLn;

TYPE Fn = PROCEDURE(CARDINAL): CARDINAL;

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

PROCEDURE M(n: CARDINAL): CARDINAL;
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: CARDINAL;
BEGIN
    WriteString(name);
    WriteString(": ");
    FOR i := 0 TO Max DO
        WriteCard(fn(i), 0);
        WriteString(" ");
    END;
    WriteLn;
END Show;

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