Question: Why does printing fix my error message?

I've got a really bizarre error. In my quite short code, if I do not have the print statement, I get the error message 'Error, (in fib_even_sum) illegal use of an object as a name'. If I do use the print statement, the code runs fine, albeit having printed an unnecessary zero.

Here's the code:

fib_even_sum := proc()::integer:

options threadsafe,autocompile:

uses combinat:

local val := 0, n := 1, FN := 0:


while FN <= 4000000 do:

if type(FN,even) then:

val += FN:

else end if:


FN := fibonacci(n):

end do:

return val:

end proc:


I can't see what would be making it behave like this; perhaps I'm missing something really obvious?

Please Wait...