Surprising whitespace behavior

steves has asked for the wisdom of the Perl Monks concerning the following question:

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Use B::Deparse to see why by htoug (Deacon) on Sep 23, 2004 at 14:05 UTC
If you try `perl -MO=Deparse` you will see that the perl compiler interprets the print statement as you surmised: `my(@a) = ('a', 'b', 'c', 'def'); my $s = 'foo'; print "s=$s, a=\@ a\n"; - syntax OK` [download] Why there is a difference between the interpretation of $ followed by whitespace and @ followed by whitespace probably lies in the fact that @-interpolation is a quite new invention (5.6 AFAICR). -MO=Deparse is very handy for finding out why a coinstruct does what it does (and for deobfuscation).	[reply] [d/l] [select]
•Re: Use B::Deparse to see why by merlyn (Sage) on Sep 23, 2004 at 14:13 UTC
probably lies in the fact that @-interpolation is a quite new invention (5.6 AFAICR). Oh, you young'uns. {grin} @-interpolation in a string dates back to Perl version 5.000. It's the reason that you get the fatal error when you have something like `"merlyn@stonehenge.com"`. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^2: Use B::Deparse to see why (age) by tye (Sage) on Sep 23, 2004 at 16:21 UTC
@-interpolation in a string dates back to Perl version 5.000. Oh, you young'uns. (: It dates back way before that. I've personally used @-interpolation in strings in Perl v3. `> perl4 -e "print qq<(tye@ARGV)\n>" this that (tyethis that) > perl4 -e "print qq<(tye@foo)\n>" this that (tye@foo)` [download] What changed with Perl5 was that the DWIM of optional interpolation was removed. The only reason the second example needs to be fatal in Perl5 is so that the change in behavior was not a "silent change". I suspect you know all of this, but your node was at least misleading so I felt clarification was in order. - tye	[reply] [d/l]
•Re^3: Use B::Deparse to see why (age) by merlyn (Sage) on Sep 23, 2004 at 16:23 UTC
Re: Use B::Deparse to see why by dragonchild (Archbishop) on Sep 23, 2004 at 14:11 UTC
5.005_3 had @-interpolation. I'm not sure about older Perls. ------ We are the carpenters and bricklayers of the Information Age. Then there are Damian modules.... sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon.* - flyingmoose I shouldn't have to say this, but any code, unless otherwise stated, is untested	[reply]
Re: Surprising whitespace behavior by QM (Parson) on Sep 23, 2004 at 18:21 UTC
Not knowing which post to reply to... So now that we've determined that "$ x" behaves differently from "@ x", why stop there? `DB<1> $x = 'DollarX' DB<2> @x = 'a'..'g' DB<3> %x = qw(1 a 2 b 3 c) DB<4> sub x { print "This is Sub x\n" } DB<5> p "<$x> <@x> <%x> <&x>" <DollarX> <a b c d e f g> <%x> <&x> DB<6> p "<$ x> <@ x> <% x> <& x>" <DollarX> <@ x> <% x> <& x> DB<7> p "$ #x" Final $ should be \$ or $name at (eval 12)[C:/Perl/lib/perl5db.pl:17] +line 2, within string syntax error at (eval 12)[C:/Perl/lib/perl5db.pl:17] line 2, near "} +"$ #x""` [download] So `"$ x"` is the only one this works for, and it breaks for `"$ #x"`, even though that looks like a scalar (and it probably shouldn't break!). But `"$ x[0]"` produces `"a"`, and so does `"$ x{1}"`. I'm sure there's some Good Reason Why This Is So...Perhaps it's easy to figure out what to do with `"$x"`, but there are more options with `"@x"`. The string interpolation aspect of ignoring whitespace was probably not updated when `"@x"` interpolation was added. [I secretly hoped Merlyn would have the skinny on that -- but I'm sure he would have said so.] -QM -- Quantum Mechanics: The dreams stuff is made of	[reply] [d/l] [select]
Re^2: Surprising whitespace behavior (significant whitespace++) by tye (Sage) on Sep 23, 2004 at 19:53 UTC
I think `"$ x"` should be `"\$ x"`. I have no problem with double-quote interpolation being more strict than the equivalent Perl code (it already is and this one more case would be an improvement). I think it is just a matter of the original implementor(s) (way back in Perl2) deciding to support ignoring such whitespace (to match how Perl works outside of double quotes) and the more recent implementor(s) (p5p) not even thinking of supporting such a strange construct (and so not worrying about making them consistent). - tye	[reply] [d/l] [select]
cool - 1 column programming by fglock (Vicar) on Sep 23, 2004 at 20:21 UTC
`$ x = " h e l l o w o r l d " ; print " $ x " ;` [download] output: `h e l l o w o r l d` [download]	[reply] [d/l] [select]


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