Hi,
Larry Wall wrote:
> On Sun, Nov 20, 2005 at 08:51:03PM +0100, Ingo Blechschmidt wrote:
> : according to the new S03, till is the new name for the flipflop
> : operator.
>
> Presuming we can make it work out as an infix macro.
Ah, it's a macro. This clarifies things.
> : Do the flipflop operators of subroutines maintain own
> : per-invocation-of-the-sub states? I.e.:
> :
> : sub foo (&x) { x() till 0 }
> :
> : foo { 0 }; # evaluates to a false value, of course
> :
> : foo { 1 }; # evaluates to a true value, of course
> : foo { 0 };
> : # still true?
> : # (Argumentation: The flipflop is in the "true" state,
> : # so the LHS is not evaluated.)
> : # Or is it false?
> : # (Argumentation: The flipflop operator of the previous
> : # invocation is not the flipflop operator of the current
> : # invocation, so the return value is false.)
>
> It's still true. Ignoring the "E0" issue, the desugar of "A till B"
> is something like:
[...]
Thanks very much, this code is very clear. :)
> : Also, all operators can be called using the subroutine form (which
> : is a very good thing), e.g.:
> :
> : say infix:<->(42, 19); # 23
> :
> : Is this true for till as well?
> :
> : say infix:<till>(LHS, RHS);
>
> Probably not. Calling macros as functions is a bit of a problem.
Yep. (I assumed &infix:<till> would be an ordinary subroutine.)
> : But how would &infix:<till> maintain the state then, as no explicit
> : ID is passed to it? Does &infix:<till> access an internal %states
> : hash, using $CALLER::POSITION as keys?
>
> That feels like a hack to me. I'd rather find a way of poking a real
> state variable into the caller's scope if we have to support that.
Agreed. The desugar you provides feels far more sane.
> : Perl 5's flipflop operator appends "E0" to the final sequence number
> : in a range, allowing searches for /E/. My guess is that this is
> : superseded by "$sequence_number but
> : this_is_the_endpoint_of_the_range" (you get the idea). Correct?
>
> I was just thinking that you'd use till^ if you wanted to exclude the
> endpoint. And ^till to exclude the beginning, and ^till^ to exclude
> both, just as with ..^, ^.., and ^..^.
Ok.
> In fact, that's really my main motivation for wanting it to be infix.
> Otherwise it might as well be an ordinary flipflip() macro, or
> fromto().
Makes sense.
--Ingo
