Comment author: administrator

This loops :

for i = 0 to max_int do
if i mod (max_int / 10) = 0 then Printf.printf "%i\n" i;
flush stdout
done;;

While that does not

let rec f i =
if i <> max_int then begin
if i mod (max_int / 10) = 0 then Printf.printf "%i\n" i;
flush stdout;
f (i + 1)
end in (f 0)

Am I missing something ?

That's a known issue -- a rather amusing one, actually. Basically, the
"for" loop in the first example is compiled into:

    let i = ref 0 in
    while (!i <= max_int) do
      ...
      i := !i + 1
    done

and the test !i <= max_int is always true by definition of max_int.
Hence the infinite loop.

Notice that your second example is not equivalent to the first: it
iterates up to max_int - 1, not up to max_int, just like
"for i = 0 to max_int - 1 do done". (And the latter terminates
without problems.)

If you try to rewrite your second example so that it iterates up to
max_int included and stop, you might realize the difficulty of
correctly compiling "for" loops with max_int as upper bound...

I agree something should be done about this, but it's not completely
trivial to fix and doesn't seem too urgent.

Best regards,

• Xavier Leroy

Comment author: administrator

Fixed 2002-11-18 by XL.