Iteration over lists
Fri Mar 17 17:57:29 CET 2006
Bjorn Gustavsson wrote:
> What you call recursion is in fact iteration expressed as tail-recursion.
> Naturally it is faster.
> Real recursion would look this:
> recursion([H | T]) ->
> [integer_to_list(H) | recursion(T)];
> recursion() -> .
> A list comprehension will in fact be translated to the exact same
> code a the function above.
> Using tail-recursion and then reversing is somewhat slower than either
> recursion or list comprehensions. My list size was 6000. I expect that
> if the lists are really huge, revrecursion will win.
Also, if each iteration does more work than just calling
integer_to_list, recursing, and consing up a new element,
it could make the stack frame size bigger, which could
significantly lower the break-even point in favour of the
tail recursive version with reverse at the end.
(This is of course assuming that the Beam compiler does not
use stack trimming techniques, but I don't think it does.)
It could be worth including such an example in the benchmarks.
/Richard "too lazy to do my own measurements" C.
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