Tiny Perl puzzle

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Re: Tiny Perl puzzle by tobyink (Canon) on Jun 05, 2014 at 22:19 UTC
<Reveal this spoiler or all in this thread> Good puzzle. This sort of thing is precisely the reason various best practices have arisen. `use Moops; class Cow :rw { has name => (default => 'Ermintrude') }; say Cow->new->name`	[reply] [d/l] [select]
Re: Tiny Perl puzzle (duh) by tye (Sage) on Jun 06, 2014 at 00:22 UTC
This surprises any even moderately experienced Perl programmer? Update: It appears that my test didn't sufficiently accurately replicate the original program text. Though I admit this particular quirk didn't and doesn't bother me much as I avoid barewords exactly because they lead to lots of ambiguities. - tye	[reply]
Re: Tiny Perl puzzle by LanX (Saint) on Jun 06, 2014 at 00:35 UTC
not sure about the precedence my first guess is "true" my second 1 Can't test ATM :) Cheers Rolf (addicted to the Perl Programming Language) update tobyinc's analysis is correct! :) one more reason to enforce `use strict` and 'warnings'...	[reply] [d/l]
Re^2: Tiny Perl puzzle by Anonymous Monk on Jun 06, 2014 at 01:16 UTC
I wasn't even trying to guess what it would really parse as so I just Deparse and run it $ perl -MO=Deparse print (two + two == five ? "true" : "false") ^Z print two 'two' == 'five' ? 'true' : 'false'; - syntax OK $ perl -MO=Deparse,-p print (two + two == five ? "true" : "false") ^Z print(two (('two' == 'five') ? 'true' : 'false')); - syntax OK $ perl -w print (two + two == five ? "true" : "false") print (...) interpreted as function at - line 1. Unquoted string "two" may clash with future reserved word at - line 1. Unquoted string "two" may clash with future reserved word at - line 1. Unquoted string "five" may clash with future reserved word at - line 1 +. ^Z Name "main::two" used only once: possible typo at - line 1. Argument "five" isn't numeric in numeric eq (==) at - line 1. Argument "two" isn't numeric in numeric eq (==) at - line 1. print() on unopened filehandle two at - line 1. [download]	[reply] [d/l]
Re^3: Tiny Perl puzzle by davido (Cardinal) on Jun 06, 2014 at 18:43 UTC
I think B::Deparse gets it wrong -- as it sometimes does -- when you add `-p`: My theory: When Deparse tries to add parens wherever it can, it treats the first `two` as a function call (which was my first guess too). But as tobyink correctly surmised, that first `two` is treated by print as a filehandle. This is confirmed by the more low-level output of B::Concise: `$ perl -MO=Concise,-exec, -e 'print ( two + two == five ? "true" : "fa +lse" )' 1 <0> enter 2 <;> nextstate(main 1 -e:1) v:{ 3 <0> pushmark s 4 <$> gv(*two) s 5 <1> rv2gv sKR/1 6 <$> const(PV "two") s/BARE 7 <$> const(PV "five") s/BARE 8 <2> eq sK/2 9 <\|> cond_expr(other->a) lK/1 a <$> const(PV "true") s goto b d <$> const(PV "false") s b <@> print vKS c <@> leave[1 ref] vKP/REFC -e syntax OK` [download] It's easy to see from this output that the first `two` is treated as a typeglob; a filehandle. The second `two` and the `five` are treated as barewords; constants in this case, which are then compared to one another. They evaluate to the same constant defined value, which is probably an empty string, equating to 0 for the purpose of numeric equality. So "true" will result, but it's printed to a filehandle that hasn't been attached to anything. Dave	[reply] [d/l] [select]
Re^4: Tiny Perl puzzle by Anonymous Monk on Jun 07, 2014 at 07:25 UTC
Re^4: Tiny Perl puzzle by LanX (Saint) on Jun 07, 2014 at 15:38 UTC
Re^5: Tiny Perl puzzle by Anonymous Monk on Jun 08, 2014 at 09:17 UTC
Some notes below your chosen depth have not been shown here
Re: Tiny Perl puzzle by locked_user sundialsvc4 (Abbot) on Jun 06, 2014 at 12:09 UTC
`print (two + two == five) ? ( user == politician) ? "Re-elect me and I will fix it." : "It's not a bug, it's a feature!" : (user == accountant) ? "What do you -want- the answer to be?" : "Don't worry, sonny, no child will be left behind.™" ;` [download]
Re^2: Tiny Perl puzzle by LanX (Saint) on Jun 06, 2014 at 13:31 UTC
Another incorrect Perl puzzle? (hint: `print` greedily loves brackets! :) Cheers Rolf (addicted to the Perl Programming Language)	[reply]
Re^2: Tiny Perl puzzle by Anonymous Monk on Jun 07, 2014 at 07:27 UTC
(Please mark spoilers accordingly.) sundialsvc4, why not honor the OPs request and use spoiler tags?	[reply]

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