factorial = proc (n: int) returns (int) signals (negative)
    if n<0 then signal negative
    elseif n=0 then return(1)
    else return(n * factorial(n-1))
    end
end factorial

start_up = proc ()
    po: stream := stream$primary_output()

    for i: int in int$from_to(0, 10) do
        fac: int := factorial(i)
        stream$putl(po, int$unparse(i) || "! = " || int$unparse(fac))
    end
end start_up