Lack of space after != operator changes behaviour

[p6rt]

Migrated from rt.perl.org#121108 (status was 'open')

Searchable as RT121108$

[p6rt]

From @peschwa

The following test in roast currently is skipped for Rakudo as a nom regression​:

{
  # Check a 3 != 3 vs 3 !=3 parsing issue that can cropped up in Rakudo.
  # Needs careful following of STD to get it right. :-)
  my $r;
  sub foo($x) { $r = $x }
  foo 3 != 3;
  is($r, False, 'sanity 3 != 3');
  foo 3 !=3;
  is($r, False, 'ensure 3 !=3 gives same result as 3 != 3');
}

STD parses the comparision successfully​:

<psch> std​: 3 !=3
<camelia> std 09dda5b​: OUTPUT«ok 00​:01 122m␤»

while Rakudo tries to assign and fails​:

<psch> r​: say 3 !=3
<camelia> rakudo-parrot c884dc​: OUTPUT«Cannot modify an immutable value␤ in sub infix​:<=> at gen/parrot/CORE.setting​:16361␤ in block at gen/parrot/CORE.setting​:16706␤ in block at /tmp/tmpfile​:1␤␤»
23​:33 <camelia> ..rakudo-moar c884dc​: OUTPUT«No such method 'STORE' for invocant of type 'Int'␤ in sub infix​:<=> at src/gen/m-CORE.setting​:16092␤ in block at src/gen/m-CORE.setting​:16436␤ in block at /tmp/tmpfile​:1␤␤»
<camelia> ..rakudo-jvm c884dc​: OUTPUT«Cannot modify an immutable value␤ in sub infix​:<=> at gen/jvm/CORE.setting​:16095␤ in block at gen/jvm/CORE.setting​:16439␤ in block at /tmp/tmpfile​:1␤␤»

[p6rt]

From @FROGGS

that STD says it is okay does not mean much here, because​:

./viv -e 'say 1 != 3'
[...]
└─VAST​::SYM_infix__S_BangEqual, BEG​: 6, END​: 8, SYM​: !=,
  TEXT​: !=, WS​: 1, _from​: 8, _op​: VAST​::infix__S_BangEqual,
  _pos​: 8, _specific​: 1, assoc​: chain, dba​: chaining,
  diffy​: 1, iffy​: 1, prec​: m=, pure​: 1
[...]

./viv -e 'say 1 !=3'
[...]
└─VAST​::SYM_infix__S_Equal, BEG​: 7, END​: 8, SYM​: =, TEXT​: =,
  _from​: 8, _op​: VAST​::infix__S_Equal, _pos​: 8,
  _specific​: 1, assoc​: right, dba​: list assignment,
  fiddly​: 1, prec​: i=, pure​: 0
[...]

So already STD has a problem here and I will open a STD-issue in its github repo, see​:
perl6/std#7

[p6rt]

The RT System itself - Status changed from 'new' to 'open'

[p6rt]

From @zoffixznet

If the programmer omits the space after the != (not equal, numeral) operator, the behavior of the operator changes to​: [assign RHS to LHS, return !RHS], as can be seen from these examples​:

<ZoffixW> m​: say 0 != 0
<camelia> rakudo-moar f05c77​: OUTPUT«False␤»
<ZoffixW> m​: say 0 !=0
<camelia> rakudo-moar f05c77​: OUTPUT«Cannot modify an immutable Int␤ in block <unit> at /tmp/7Z5OWfl3Go line 1␤␤»
<ZoffixW> m​: my $x = 42; say $x !=0; say $x
<camelia> rakudo-moar f05c77​: OUTPUT«True␤0␤»
<ZoffixW> m​: my $x = 0; say $x !=42; say $x
<camelia> rakudo-moar f05c77​: OUTPUT«False␤42␤»

This behaviour is confusing and probably not wanted by most programmers.

[p6rt]

From @peschwa

On Mon Apr 25 09​:20​:43 2016, cpan@​zoffix.com wrote​:

If the programmer omits the space after the != (not equal, numeral)
operator, the behavior of the operator changes to​: [assign RHS to LHS,
return !RHS], as can be seen from these examples​:

<ZoffixW> m​: say 0 != 0
<camelia> rakudo-moar f05c77​: OUTPUT«False␤»
<ZoffixW> m​: say 0 !=0
<camelia> rakudo-moar f05c77​: OUTPUT«Cannot modify an immutable Int␤
in block <unit> at /tmp/7Z5OWfl3Go line 1␤␤»
<ZoffixW> m​: my $x = 42; say $x !=0; say $x
<camelia> rakudo-moar f05c77​: OUTPUT«True␤0␤»
<ZoffixW> m​: my $x = 0; say $x !=42; say $x
<camelia> rakudo-moar f05c77​: OUTPUT«False␤42␤»

This behaviour is confusing and probably not wanted by most
programmers.

This is a dupe of https://rt-archive.perl.org/perl6/Ticket/Display.html?id=121108, which is wrongly titled at the moment.

[p6rt]

The RT System itself - Status changed from 'new' to 'open'

[lizmat]

Fixed with rakudo/rakudo@12dd09e1b4