Piers Cawley wrote:
[snip]
> Um... no. tail call optimization implies being able to replace *any*
> tail call, not just a recursive one with a simple goto.
[snip]
In perl5, doing a tail call optimization can be done with just a simple
goto... well, 'goto &subname', anyway. (Well, first you'd assign
something to @_, then goto &subname).
Since (supposedly) there's going to be a perl5->parrot compiler, there
needs to be support for perl5's goto &subname. ISTM that once we have
figured out an efficient way of implementing that, we'll also have an
efficient way of doing native tail call optimization.
As a wild-ass-guess, an optimized tail call will look something like:
.sub _foo # sub foo(int a, int b)
saveall
.param int a # a = pop @_
.param int b # b = pop @_
...
.arg int x # push @_, x
.arg int u # push @_, u
.arg int q # push @_, q
restoreall
jnsr _bar # goto &_bar
.end
.sub _bar # sub bar(int q, int u, int x) {
saveall
.param int q # q = pop @_
.param int u # u = pop @_
.param int x # x = pop @_
...
.return int pl # push @_, pl
.return int ml # push @_, ml
restoreall
ret
.end
The 'jnsr' opcode (JumpNoSaveReturn) might be spelled as 'j' or as
'goto', or something else entirely, depending on what's least confusing,
and most aesthetically pleasing.
--
$;=qq qJ,krleahciPhueerarsintoitq;sub __{0 &&
my$__;s ee substr$;,$,&&++$__%$,--,1,qq;;;ee;
$__>2&&&__}$,=22+$;=~y yiy y;__ while$;;print
