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Documentation "The Ellipsis Statement" of perlsyn #14054

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p5pRT opened this issue Aug 31, 2014 · 12 comments
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@p5pRT p5pRT commented Aug 31, 2014

Migrated from rt.perl.org#122661 (status was 'resolved')

Searchable as RT122661$

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@p5pRT p5pRT commented Aug 31, 2014

From ina.cpan@gmail.com

This is a bug report for perl from ina.cpan@​gmail.com,
generated with the help of perlbug 1.40 running under perl 5.20.0.


The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

But results are​:

C​:\>c​:\strawberry\perl520\bin\perl -ce "map{;...}()"
-e syntax OK

C​:\>c​:\strawberry\perl520\bin\perl -ce "map{...;}()"
syntax error at -e line 1, near "{..."
-e had compilation errors.



Flags​:
category=docs
severity=low


Site configuration information for perl 5.20.0​:

Configured by strawberry-perl at Fri May 30 23​:27​:10 2014.

Summary of my perl5 (revision 5 version 20 subversion 0) configuration​:

Platform​:
osname=MSWin32, osvers=6.2, archname=MSWin32-x86-multi-thread-64int
uname='Win32 strawberry-perl 5.20.0.1 #1 Fri May 30 23​:25​:11 2014 i386'
config_args='undef'
hint=recommended, useposix=true, d_sigaction=undef
useithreads=define, usemultiplicity=define
use64bitint=define, use64bitall=undef, uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler​:
cc='gcc', ccflags =' -s -O2 -DWIN32 -DPERL_TEXTMODE_SCRIPTS
-DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -DUSE_PERLIO -fwrapv
-fno-strict-aliasing -mms-bitfields',
optimize='-s -O2',
cppflags='-DWIN32'
ccversion='', gccversion='4.8.2', gccosandvers=''
intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
ivtype='long long', ivsize=8, nvtype='double', nvsize=8, Off_t='long long',
lseeksize=8
alignbytes=8, prototype=define
Linker and Libraries​:
ld='g++', ldflags ='-s -L"C​:\strawberry\perl\lib\CORE"
-L"C​:\strawberry\c\lib"'
libpth=C​:\strawberry\c\lib C​:\strawberry\c\i686-w64-mingw32\lib
C​:\strawberry\c\lib\gcc\i686-w64-mingw32\4.8.2
libs=-lmoldname -lkernel32 -luser32 -lgdi32 -lwinspool -lcomdlg32
-ladvapi32 -lshell32 -lole32 -loleaut32 -lnetapi32 -luuid -lws2_32 -lmpr
-lwinmm -lversion -lodbc32 -lodbccp32 -lcomctl32
perllibs=-lmoldname -lkernel32 -luser32 -lgdi32 -lwinspool -lcomdlg32
-ladvapi32 -lshell32 -lole32 -loleaut32 -lnetapi32 -luuid -lws2_32 -lmpr
-lwinmm -lversion -lodbc32 -lodbccp32 -lcomctl32
libc=, so=dll, useshrplib=true, libperl=libperl520.a
gnulibc_version=''
Dynamic Linking​:
dlsrc=dl_win32.xs, dlext=xs.dll, d_dlsymun=undef, ccdlflags=' '
cccdlflags=' ', lddlflags='-mdll -s -L"C​:\strawberry\perl\lib\CORE"
-L"C​:\strawberry\c\lib"'


@​INC for perl 5.20.0​:
C​:/strawberry/perl520/site/lib
C​:/strawberry/perl520/vendor/lib
C​:/strawberry/perl520/lib
.


Environment for perl 5.20.0​:
HOME (unset)
LANG (unset)
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=C​:\Perl\bin\MSWin32-x86-object;C​:\Perl\bin;C​:\WINDOWS\system32;C​:\WINDOWS;C​:\WINDOWS\System32\Wbem;c​:\Program
Files\Intel\DMIX
PERL_BADLANG (unset)
SHELL (unset)

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@p5pRT p5pRT commented Aug 31, 2014

From @jkeenan

On Sun Aug 31 00​:43​:58 2014, ina.cpan@​gmail.com wrote​:

This is a bug report for perl from ina.cpan@​gmail.com,
generated with the help of perlbug 1.40 running under perl 5.20.0.

-----------------------------------------------------------------
The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

But results are​:

C​:\>c​:\strawberry\perl520\bin\perl -ce "map{;...}()"
-e syntax OK

C​:\>c​:\strawberry\perl520\bin\perl -ce "map{...;}()"
syntax error at -e line 1, near "{..."
-e had compilation errors.

And here's confirmation of the bug with the example code found in 'perlsyn'​:
#####
$ cat 122661.pl
my @​input = qw( alpha beta gamma );
my @​transformed = map { ...; } @​input;

$ perl 122661.pl
syntax error at 122661.pl line 2, near "{ ..."
Execution of 122661.pl aborted due to compilation errors.
#####

My hunch would be that in the case of { ...; } perl is not recognizing ... as the ellipsis statemente but rather as the flip-flop operator.

If I use perlbrew to switch to older versions of perl, I get exactly the same syntax error output in versions older than the ellipsis statement.

#####
$ perlbrew switch perl-5.14.4
$ perl 122661.pl
syntax error at 122661.pl line 2, near "{ ..."
Execution of 122661.pl aborted due to compilation errors.

$ perlbrew switch perl-5.10.1
$ perl 122661.pl
syntax error at 122661.pl line 2, near "{ ..."
Execution of 122661.pl aborted due to compilation errors.

$ perlbrew switch perl-5.8.9
$ perl 122661.pl
syntax error at 122661.pl line 2, near "{ ..."
Execution of 122661.pl aborted due to compilation errors.
#####

Thank you very much.
Jim Keenan

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@p5pRT p5pRT commented Aug 31, 2014

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

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@p5pRT p5pRT commented Sep 3, 2014

From @rjbs

* ina cpan <perlbug-followup@​perl.org> [2014-08-31T03​:43​:59]

-----------------------------------------------------------------
The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

I am somewhat baffled, as I have never seen "put semicolon at the end" used for
this purpose. It didn't work in v5.12.5. I think this is probably just a
documentation error, plain and simple, yes?

--
rjbs

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@p5pRT p5pRT commented Sep 3, 2014

From @ikegami

On Tue, Sep 2, 2014 at 9​:31 PM, Ricardo Signes <perl.p5p@​rjbs.manxome.org>
wrote​:

I am somewhat baffled, as I have never seen "put semicolon at the end"
used for
this purpose. It didn't work in v5.12.5. I think this is probably just a
documentation error, plain and simple, yes?

Correct. Documentation error.

Nothing to do with "..."

perl -e"map { 1, $_; } @​a"
syntax error at -e line 1, near "; }"
Execution of -e aborted due to compilation errors.

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@p5pRT p5pRT commented Sep 3, 2014

From ina.cpan@gmail.com

I think so too.

2014-09-03 10​:31 GMT+09​:00 Ricardo Signes via RT <perlbug-followup@​perl.org>
:

* ina cpan <perlbug-followup@​perl.org> [2014-08-31T03​:43​:59]

-----------------------------------------------------------------
The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

I am somewhat baffled, as I have never seen "put semicolon at the end"
used for
this purpose. It didn't work in v5.12.5. I think this is probably just a
documentation error, plain and simple, yes?

--
rjbs

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@p5pRT p5pRT commented Sep 13, 2014

From @jkeenan

On Tue Sep 02 18​:31​:46 2014, perl.p5p@​rjbs.manxome.org wrote​:

* ina cpan <perlbug-followup@​perl.org> [2014-08-31T03​:43​:59]

-----------------------------------------------------------------
The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

I am somewhat baffled, as I have never seen "put semicolon at the end"
used for
this purpose. It didn't work in v5.12.5. I think this is probably
just a
documentation error, plain and simple, yes?

In order to move this ticket toward resolution, I have prepared the patch attached. Please review.

Thank you very much.

--
James E Keenan (jkeenan@​cpan.org)

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@p5pRT p5pRT commented Sep 13, 2014

From @jkeenan

0001-Semicolon-before-ellipsis-inside-block-disambiguates.patch
From a10e023e280a942393a96816c96bae288a77f9d4 Mon Sep 17 00:00:00 2001
From: James E Keenan <jkeenan@cpan.org>
Date: Sat, 13 Sep 2014 08:51:48 -0400
Subject: [PATCH] Semicolon before ellipsis inside block disambiguates.

Correct documentation which indicated that, inside a block, a semicolon after
an ellipsis statement would disambiguate between a block and a hash reference
constructor.  The semicolon must precede the ellipsis to perform this
disambiguation.

Add tests to demonstrate that whitespace around the ellipsis statement does
not impeded the disambiguation.

For: RT #122661
---
 pod/perlsyn.pod | 11 +++++------
 t/op/yadayada.t | 31 ++++++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/pod/perlsyn.pod b/pod/perlsyn.pod
index cea4d50..73421a4 100644
--- a/pod/perlsyn.pod
+++ b/pod/perlsyn.pod
@@ -788,14 +788,13 @@ syntax error if Perl doesn't guess that the C<{ ... }> is a block.  In that
 case, it doesn't think the C<...> is an ellipsis because it's expecting an
 expression instead of a statement:
 
-    @transformed = map { ... } @input;  # syntax error
+    @transformed = map { ... } @input;    # syntax error
 
-You can use a C<;> inside your block to denote that the C<{ ...  }> is a
-block and not a hash reference constructor.  Now the ellipsis works:
+Inside your block, you can use a C<;> before the ellipsis to denote that the
+C<{ ... }> is a block and not a hash reference constructor.  Now the ellipsis
+works:
 
-    @transformed = map {; ... } @input; # ; disambiguates
-
-    @transformed = map { ...; } @input; # ; disambiguates
+    @transformed = map {; ... } @input;   # ';' disambiguates
 
 Note: Some folks colloquially refer to this bit of punctuation as a
 "yada-yada" or "triple-dot", but its true name
diff --git a/t/op/yadayada.t b/t/op/yadayada.t
index 770a51e..a213bec 100644
--- a/t/op/yadayada.t
+++ b/t/op/yadayada.t
@@ -8,14 +8,39 @@ BEGIN {
 
 use strict;
 
-plan 5;
+plan 9;
 
-my $err = "Unimplemented at $0 line " . ( __LINE__ + 2 ) . ".\n";
+my $err;
+my $err1 = "Unimplemented at $0 line ";
+my $err2 = ".\n";
 
+$err = $err1 . ( __LINE__ + 1 ) . $err2;
 eval { ... };
+is $@, $err, "Execution of ellipsis statement reported 'Unimplemented' code";
+$@ = '';
 
-is $@, $err;
+note("RT #122661: Semicolon before ellipsis statement disambiguates to indicate block rather than hash reference");
+my @input = (3..5);
+my @transformed;
+$err = $err1 . ( __LINE__ + 1 ) . $err2;
+eval { @transformed = map {; ... } @input; };
+is $@, $err, "Disambiguation case 1";
+$@ = '';
 
+$err = $err1 . ( __LINE__ + 1 ) . $err2;
+eval { @transformed = map {;...} @input; };
+is $@, $err, "Disambiguation case 2";
+$@ = '';
+
+$err = $err1 . ( __LINE__ + 1 ) . $err2;
+eval { @transformed = map {; ...} @input; };
+is $@, $err, "Disambiguation case 3";
+$@ = '';
+
+$err = $err1 . ( __LINE__ + 1 ) . $err2;
+eval { @transformed = map {;... } @input; };
+is $@, $err, "Disambiguation case 4";
+$@ = '';
 
 #
 # Regression tests, making sure ... is still parsable as an operator.
-- 
1.9.1

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@p5pRT p5pRT commented Sep 13, 2014

From @demerphq

On 3 September 2014 06​:50, Eric Brine <ikegami@​adaelis.com> wrote​:

On Tue, Sep 2, 2014 at 9​:31 PM, Ricardo Signes <perl.p5p@​rjbs.manxome.org>
wrote​:

I am somewhat baffled, as I have never seen "put semicolon at the end"
used for
this purpose. It didn't work in v5.12.5. I think this is probably just a
documentation error, plain and simple, yes?

Correct. Documentation error.

Nothing to do with "..."

perl -e"map { 1, $_; } @​a"
syntax error at -e line 1, near "; }"
Execution of -e aborted due to compilation errors.

I think you could argue this is a bug too, although in the same category as
this​:

perl -le'map { no warnings; $x++ } 1..10'
"no" not allowed in expression at -e line 1, at end of line
BEGIN not safe after errors--compilation aborted at -e line 1.

That is the parser thinks the open { is the beginning of a hash constructor.

This works​:

perl -le'map {; no warnings; $x++ } 1..10'

because the {; tells the parser early enough "this can't be a hash
constructor".

Personally I would love to see a "once and for all" fix to this class of
stupid.

Yves

--
perl -Mre=debug -e "/just|another|perl|hacker/"

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@p5pRT p5pRT commented Sep 13, 2014

From @cpansprout

On Sat Sep 13 06​:07​:36 2014, jkeenan wrote​:

On Tue Sep 02 18​:31​:46 2014, perl.p5p@​rjbs.manxome.org wrote​:

* ina cpan <perlbug-followup@​perl.org> [2014-08-31T03​:43​:59]

-----------------------------------------------------------------
The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html
said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

I am somewhat baffled, as I have never seen "put semicolon at the
end"
used for
this purpose. It didn't work in v5.12.5. I think this is probably
just a
documentation error, plain and simple, yes?

In order to move this ticket toward resolution, I have prepared the
patch attached. Please review.

Your patch is good.

--

Father Chrysostomos

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@p5pRT p5pRT commented Sep 13, 2014

From @jkeenan

On Sat Sep 13 06​:46​:05 2014, sprout wrote​:

On Sat Sep 13 06​:07​:36 2014, jkeenan wrote​:

On Tue Sep 02 18​:31​:46 2014, perl.p5p@​rjbs.manxome.org wrote​:

* ina cpan <perlbug-followup@​perl.org> [2014-08-31T03​:43​:59]

-----------------------------------------------------------------
The Ellipsis Statement of http​://perldoc.perl.org/perlsyn.html
said,

You can use a ; inside your block to denote that the { ... } is a
block and not a hash reference constructor. Now the ellipsis works​:

1. @​transformed = map {; ... } @​input; # ; disambiguates
2.
3. @​transformed = map { ...; } @​input; # ; disambiguates

I am somewhat baffled, as I have never seen "put semicolon at the
end"
used for
this purpose. It didn't work in v5.12.5. I think this is probably
just a
documentation error, plain and simple, yes?

In order to move this ticket toward resolution, I have prepared the
patch attached. Please review.

Your patch is good.

Thanks for the review. Applied to blead in
commit 12d22d1

Marking ticket resolved.

--
James E Keenan (jkeenan@​cpan.org)

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@p5pRT p5pRT commented Sep 13, 2014

@jkeenan - Status changed from 'open' to 'resolved'

@p5pRT p5pRT closed this Sep 13, 2014
@p5pRT p5pRT added the Severity Low label Oct 19, 2019
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