Can't see the syntax error here...

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

Dear Monks,

could someone kindly explain to me, why this innocent little program is syntactically wrong?

use strict;
use warnings;

my $xnix='X';

sub f {
  {$xnix => 100}->{'X'}
}

print f(),"\n";
[download]

ActiveState Perl complains:

syntax error at U:\develsv\ARTS\playground\hash_problem.pl line 7, nea
+r "}->"
syntax error at U:\develsv\ARTS\playground\hash_problem.pl line 8, nea
+r "}"
[download]

The problem must be related to the usage in a sub, because the similar

use strict;
use warnings;
my $xnix='X';
my $f={$xnix => 100}->{'X'};
print $f,"\n";
[download]

works as expected.

--
Ronald Fischer <ynnor@mm.st>

Comment on Can't see the syntax error here... Select or Download Code

Replies are listed 'Best First'.
Re: Can't see the syntax error here... by moritz (Cardinal) on Jun 13, 2008 at 11:54 UTC
Perl tries to parse the curly braces as a block, not a hash ref. Use a + to disambiguate: `+{$xnix => 100}->{'X'}` Update: BTW this is not related to the sub at all, since a simple `print {$xnix => 100}->{'X'};` gives the same error.	[reply] [d/l] [select]
Re^2: Can't see the syntax error here... by rovf (Priest) on Jun 16, 2008 at 08:04 UTC
Amazing! I think I would searched for this for years, but once I see your explanation, it becomes clear. BTW, the reason why I thought it would be related to sub is that the similar code `my $f={$xnix => 100}->{'X'};` [download] works fine, but of course now this is clear too: In the latter case, there is no ambiguity, so it is correctly parsed as a hash. Thanks a lot for helping! -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l]
Re: Can't see the syntax error here... by andreas1234567 (Vicar) on Jun 13, 2008 at 12:00 UTC
chromatic wrote What's Wrong with Perl 5: When is a block a block, and when is it a hash reference? Seems like your problem illustrates this point. `$ perl use strict; use warnings; my $xnix='X'; sub f { my $z = {$xnix => 100}->{'X'}; # make it a hash reference return $z; } print f(),"\n"; __END__ 100` [download] -- No matter how great and destructive your problems may seem now, remember, you've probably only seen the tip of them. [1]	[reply] [d/l]