Perl parser gets confused with call to "sort" w/o parens

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

IIRC the PBP advises to omit parens when unambiguously calling built-ins, because (and I agree) it removes extra-noise and improves readability. Thus, CL#1 is written as it was and it runs OK.

Then, looking at CL#2, I thought to omit a pair of parens -- see CL#3. I don't see anything becoming ambiguous, but Perl is confused -- see CL#4. And why the uniq imposes numeric context?

Also curious, if I'm explicitly imposing numeric context on sort (CL#5), Perl warns me 6 times, and not 5, as with CL#3.

>perl -lwe "sub x{@_} print sort x( qw( q w e r t y ))"
eqrtwy

>perl -MList::Util=uniq -lwe "print sort( uniq( qw( q w e r t y )))"
eqrtwy

>perl -MList::Util=uniq -lwe "print sort uniq( qw( q w e r t y ))"
Argument "w" isn't numeric in sort at -e line 1.
Argument "r" isn't numeric in sort at -e line 1.
Argument "y" isn't numeric in sort at -e line 1.
Argument "e" isn't numeric in sort at -e line 1.
Argument "t" isn't numeric in sort at -e line 1.
qwerty

>perl -MO=Deparse -MList::Util=uniq -lwe "print sort uniq( qw( q w e r
+ t y ))"
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
use List::Util (split(/,/, 'uniq', 0));
print((sort uniq 'q', 'w', 'e', 'r', 't', 'y'));
-e syntax OK

>perl -lwe "print sort {$a <=> $b} qw( q w e r t y )"
Argument "q" isn't numeric in sort at -e line 1.
Argument "w" isn't numeric in sort at -e line 1.
Argument "e" isn't numeric in sort at -e line 1.
Argument "r" isn't numeric in sort at -e line 1.
Argument "t" isn't numeric in sort at -e line 1.
Argument "y" isn't numeric in sort at -e line 1.
qwerty
[download]

Comment on Perl parser gets confused with call to "sort" w/o parens Select or Download Code

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Re: Perl parser gets confused with call to "sort" w/o parens by choroba (Cardinal) on May 16, 2018 at 11:09 UTC
This is documented in sort: Warning: syntactical care is required... `print sort uniq( qw( q w e r t y ));` [download] Is interpreted as `print sort uniq qw( q w e r t y );` [download] i.e. it uses `uniq` as the sorting function. Update: In Perl 5.18.2., I'm not getting the numeric behaviour, it just fails with `Sort subroutine didn't return single value at -e line 1.` [download] In blead perl, though, I'm getting the same warning as you. Update 2: The numeric context is forced even when I use `uniqstr` instead of `uniq`. That's probably because Perl first calls `uniq 'q', 'w';` [download] which returns `'q', 'w'`, and sort tries to use this value as -1, 0, or 1, etc. This enforces the scalar numeric context probably. ($q=q:Sq=~/;[c](.)(.)/;chr(-\|\|-\|5+lengthSq)`"S\|oS2"`map{chr \|+ord }map{substrSq`S_+\|`\|}3E\|-\|`7**2-3:)=~y+S\|`+$1,++print+eval$q,q,a, [download]	[reply] [d/l] [select]
Re^2: Perl parser gets confused with call to "sort" w/o parens by vr (Curate) on May 16, 2018 at 11:29 UTC
:( Oh, indeed, it's documented, thanks. Yet, CL#1 works OK, and the reason why Perl can be confused here and care is required is neither clear nor explained, in documentation. How CL#4 can be parsed to what's printed out, is unclear. OK, just a thought... Edit: OK, CL#1 was parsed specially because there was single letter identifier: `>perl -lwe "sub x{@_} print sort x(qw(q w e r t y))" eqrtwy >perl -lwe "sub xx{@_} print sort xx(qw(q w e r t y))" qwerty` [download]	[reply] [d/l]
Re^3: Perl parser gets confused with call to "sort" w/o parens by BillKSmith (Monsignor) on May 16, 2018 at 14:53 UTC
The paragraph that choroba cites, documents four acceptable ways to sort an array returned by a function. I think it is reasonable to assume that anything else is ambiguous and should be considered invalid. In this view, all of your cases are invalid. The fact that some of them appear to do what you intend is irrelevant. It would be helpful if the document explained the reason for this restriction. Bill	[reply]


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