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in reply to Re: How's your Perl?
in thread How's your Perl?

1. yes

2. no and yes (perl treats while1 as one identifier)

3a. yes

8a. yes, cool, unexpected solution :-)   our official version uses a much much more obscure trick.. funny we never saw this one
Try this instead: eval(q[$$foo]) ne eval(q["$$foo"])
•Update: actually, no, the original was fine too.. even though $$foo and $$foo + 0 print differently, they don't compare numerically unequal, which is what the exercise was

11. doesn't appear to work for me..

% perl -e 'sub STDOUT{\*STDOUT} <STDOUT> eq <+STDOUT> or die'
Died at -e line 1.

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12. yes, but why? :-)

•Update: fixed the "try this".. initially said "!=" instead of "ne"

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Re: Re: Re: How's your Perl?
by BrowserUk (Patriarch) on Oct 28, 2003 at 02:30 UTC
    12. yes, but why? :-)

    I missed this before.

    For the same reason that these give a similar error 

    D:\TEMP>perl -e"sub f{'fred'} goto +f"
Can't find label SCALAR(0x15d7c1c) at -e line 1.

D:\TEMP>perl -e"sub f{'fred'} goto(f)"
Can't find label SCALAR(0x15d7c1c) at -e line 1.

D:\TEMP>perl -e"sub f{'fred'} goto f->()"
Can't find label SCALAR(0x15d7c1c) at -e line 1.

    [download]

    But these do not ;^) 

    D:\TEMP>perl -e"sub f{'fred'} goto ~~f"
Can't find label fred at -e line 1.

D:\TEMP>perl -e"sub f{'fred'} goto ''.f"
Can't find label fred at -e line 1.

D:\TEMP>perl -e"sub f{'fred'} goto scalar f"
Can't find label fred at -e line 1.

D:\TEMP>perl -e"sub f{'fred'} goto ${\f}"
Can't find label fred at -e line 1.

    [download]
    Examine what is said, not who speaks.
    "Efficiency is intelligent laziness." -David Dunham
    "Think for yourself!" - Abigail
    Hooray!
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      For the same reason that these give a similar error

      Yes but why ?   :-)

      Juerd found this one originally, and while it was obviously a parser bug, it initially puzzled us how it managed to produce that reference. (Because it takes a walk through the perl source code to truly understand the issue, I made it a bonus exercise instead of a regular one)

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        I will finally admit :) that whilst I think I know the When and the Where, I haven't a clue as to the Why! 

        P:\test>perl -MO=Concise  -e"sub f{}; goto +f"
b  <@> leave[t1] vKP/REFC ->(end)
3     <0> enter ->4
4     <;> nextstate(main 2 -e:1) v ->5
a     <1> goto vKS/1 ->b
9        <1> refgen sK/1 ->a  ## <<<HERE.
-           <1> ex-list lKRM ->9
5              <0> pushmark sRM ->6
8              <1> entersub[t2] lKRMS/NO(),TARG,INARGS,1 ->9
-                 <1> ex-list lK ->8
6                    <0> pushmark s ->7
-                    <1> ex-rv2cv sK/129 ->-
7                       <#> gv s ->8
-e syntax OK

        [download]

        Even wading through pp_goto, I couldn't quite work out why it only happens if the function is called in a list context, or indeed why it takes a reference at all. Gut feel tells me its something to do with the fact that the code tries for the goto SUB; variation prior to the goto -LABEL and goto -EXPR variations, and that something is being stacked and not cleaned up, but that's about as far as I got before my brain went into overload.

        One good thing came out of it. I now have a much better appreciation of why goto \&func is so gaddamn slow. All that chundering around unwinding stack frames, validating the target isn't a prohibited one etc. I never imagined. I'd always invisioned a simple longjump().

        Examine what is said, not who speaks.
        "Efficiency is intelligent laziness." -David Dunham
        "Think for yourself!" - Abigail
        Hooray!
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