[polyml] Question about possible compiler optimization

Lukas Bulwahn wrote:

I was mistaken that this function is tail recursive. But I was expecting that the function can be translated to the following C code (using no stack allocations):

while (p is not Nil) do if (value of p == l) then p := p->next; else break; od if (p is Nil) then raise Error...

So, this program should not allocate any stack.

That is a different function. It doesn't return the modified list but merely checks that the item is or is not present. The equivalent, tail-recursive function in ML is:

fun test l [] = raise Fail "Not present" | test l (x::xs) = if l = x then () else test l xs;

Poly/ML detects this as tail-recursive and turns it into a loop.

David