define Y(f);
    procedure (x); x(x) endprocedure(
        procedure (y);
            f(procedure(z); (y(y))(z) endprocedure)
        endprocedure
    )
enddefine;

define fac(h);
    procedure (n);
       if n = 0 then 1 else n * h(n - 1) endif
    endprocedure
enddefine;

define fib(h);
    procedure (n);
        if n < 2 then 1 else h(n - 1) + h(n - 2) endif
    endprocedure
enddefine;

Y(fac)(5) =>
Y(fib)(5) =>