Why do I need parentheses here?

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

use strict;
use warnings;
sub func {}
func ? '-N ' : '';
[download]

yields Search pattern not terminated or ternary operator parsed as search pattern. The error goes away if I call the function as func(). My question: Why does a question mark after a bareword parse as search pattern? Is it just to comply with those internal functions such as grep or split, which accept a regexp as first argument, or is there a deeper reason for this seemingly oddity?

--
Ronald Fischer <ynnor@mm.st>

Comment on Why do I need parentheses here? Select or Download Code

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Re: Why do I need parentheses here? by ikegami (Patriarch) on May 27, 2009 at 13:19 UTC
"`?`" can start both a term (`?PATTERN?`) and an operator (the conditional operator). Perl has no way of knowing which one you intended here. Since it followed a sub call, Perl assumed you were specifying arguments, so it treated the "`?`" as the start of a term. Same goes for "`/`", unary-"`-`" and unary-"`+`". Solutions: `func() ? '-N ' : ''` [download] `(func) ? '-N ' : ''` [download] `sub func() {} func ? '-N ' : ''` [download] Is it just to comply with those internal functions such as grep or split, which accept a regexp as first argument, or is there a deeper reason for this seemingly oddity? No. `func ?PATTERN?;` is no different than `func $x+1;` (and even more similar to `func -3;`). There's nothing special (or odd) about it.	[reply] [d/l] [select]
Re^2: Why do I need parentheses here? by rovf (Priest) on May 27, 2009 at 13:57 UTC
func ?PATTERN?; is no different than func $x+1;. There's nothing special (or odd) about it. I think I got it. So `func ?PAT?` is just another way of writing `func($_ =~ ?PAT?)` [download] -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l] [select]
Re^3: Why do I need parentheses here? by ikegami (Patriarch) on May 27, 2009 at 14:17 UTC
Yes. `?PAT?` and `$_ =~ ?PAT?` are equivalent, just like `/PAT/` and `$_ =~ /PAT/` are. (Aforementioned `split` is exceptional since it treats `/PAT/` as `qr/PAT/` or similar.)	[reply] [d/l] [select]
Re^4: Why do I need parentheses here? by rovf (Priest) on May 27, 2009 at 14:57 UTC
Re^5: Why do I need parentheses here? by ikegami (Patriarch) on May 27, 2009 at 15:01 UTC
Some notes below your chosen depth have not been shown here
Re^3: Why do I need parentheses here? by Anonymous Monk on May 27, 2009 at 14:01 UTC
Checking ;) `C:\>perl -MO=Deparse,-p -e"sub foo{} foo ?bar? sub foo { } foo(?bar?); -e syntax OK` [download] Yes	[reply] [d/l]
Re: Why do I need parentheses here? by jettero (Monsignor) on May 27, 2009 at 13:14 UTC
If you give func a prototype, you probably don't: `sub func() {} # and it'll probably work.` -Paul	[reply] [d/l]