On Sat, 9 Aug 2003, Benjamin Goldberg wrote:
> Michal Wallace wrote:
> [snip]
> > def f():
> > return g()
> [snip]
> > # f from line 3
> > .pcc_sub _sub1 non_prototyped
> > .local object res1 # (visitReturn:528)
> > find_lex $P2, 'g' # (callingExpression:325)
> > newsub $P3, .Continuation, ret0# (callingExpression:331)
> > .pcc_begin non_prototyped # (callingExpression:332)
> > .pcc_call $P2, $P3 # (callingExpression:335)
> > ret0:
> > .result res1 # (callingExpression:338)
> > .pcc_end # (callingExpression:339)
> > .pcc_begin_return # (visitReturn:530)
> > .return res1 # (visitReturn:531)
> > .pcc_end_return # (visitReturn:532)
> > .end
>
> Does python allow tail calls to be optomized? That is, would it be
> legal python semantics if f were to become:
>
> .pcc_sub _sub1 non_prototyped
> find_lex $P2, 'g'
> .pcc_begin non_prototyped
> .pcc_call $P2, P1
> .pcc_end
> .end
Well, the "real" python doesn't optimize tail-calls at all.
You'll get a nasty "max recursion depth exceeded" traceback
if you try running "def f(x): return f(x+1)"
But I don't see any reason pirate shouldn't do it, since the
difference is pretty much transparent.
> (untested)
> Also... why is $P2 merely an imcc temporary, without a real name? That
> is, why not do:
>
> .pcc_sub _sub1 non_prototyped
> .local object sub1
> find_lex sub1, 'g'
> .pcc_begin non_prototyped
> .pcc_call sub1, P1
> .pcc_end
> .end
>
> The more different prefixes you use ("res", "sub", "$P"), the lower the
> numbers you'll need to append to them to make the names unique. Not to
> mention, it'll make the generated code more meaningful.
>
> Another advantage is that with '.local' names, if you accidentally use a
> name declared in one subroutine, in another, imcc will consider this to
> be an error. Such a mistake might be otherwise difficult to spot.
Hmmm. The counters are global so there shouldn't be any conflicts.
I'd actually been trying to move away from .local now that I started
using lexicals... If there's going to be two sets of names for
everything I'd rather one of them was just $Pxx...
Now, if I could say:
.lexical g
That would be really nice... :)
Sincerely,
Michal J Wallace
Sabren Enterprises, Inc.
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