Re^3: Tiny Perl puzzle

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

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Re^4: Tiny Perl puzzle by Anonymous Monk on Jun 07, 2014 at 07:25 UTC
Look at the way Deparse uses whitespace, its subtle 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. That is not the way I read it :) Usually, Deparse doesn't add extraneous space to function calls, its always "foo( ... )" its never "foo ( ... )" so the way I read that deparse output is as filehandle not function call For example `$ perl -MO=Deparse 2 sub two { rand; } print two(two() == 'five' ? 'true' : 'false'); 2 syntax OK $ perl -MO=Deparse,-p 2 sub two { (rand); } print(two(((two() == 'five') ? 'true' : 'false'))); 2 syntax OK` [download] When I look at Re^2: Tiny Perl puzzle I see `print( filehandle ... );`	[reply] [d/l] [select]
Re^4: Tiny Perl puzzle by LanX (Saint) on Jun 07, 2014 at 15:38 UTC
I don't think so. did you recompile the output? I can't test ATM, but most likely it depends if a function is known at compile time. Contrary to AnoMonk I doubt space matters. Anyway IMHO the indirect object syntax should be deprecated.... Cheers Rolf (addicted to the Perl Programming Language)	[reply]
Re^5: Tiny Perl puzzle by Anonymous Monk on Jun 08, 2014 at 09:17 UTC
I can't test ATM You gotta stop saying that :) Contrary to AnoMonk I doubt space matters. Sure it does, it matters how Deparse places the space, because it matters to perl `$ perl -w print(two (('two' == 'five') ? 'true' : 'false')); Unquoted string "two" 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] That is exactly as deparsed with -p, behaves exactly like the original	[reply] [d/l]
Re^6: Tiny Perl puzzle by LanX (Saint) on Jun 08, 2014 at 13:33 UTC
> Sure it does, it matters how Deparse places the space, because it matters to perl it depends! ;-) > > most likely it depends if a function is known at compile time `> perl open ONE, ">", "/tmp/tst"; sub ONE { "@_ \n Space doesn't matter! \n" } print ONE ( TWO ); # sub-call __END__ TWO Space doesn't matter!` [download] update ALSO: `> perl open ONE, ">", "/tmp/tst"; print (ONE (TWO)); # filehandle __END__ > cat /tmp/tst TWO >` [download] BUT: `> perl open ONE, ">", "/tmp/tst"; print ONE(TWO); # sub-call __END__ Undefined subroutine &main::ONE called at - line 3.` [download] Cheers Rolf (addicted to the Perl Programming Language)	[reply] [d/l] [select]

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