[PATCH] perlop: words before a fat arrow comma can start with -

[p5pRT]

Migrated from rt.perl.org#133873 (status was 'open')

Searchable as RT133873$

[p5pRT]

From dot@dotat.at

This is a bug report for perl from dot@​dotat.at,
generated with the help of perlbug 1.41 running under perl 5.29.9.

---

I was checking whether '-' is allowed inside barewords before
fat arrows, as well as at the start of the bareword, and I
saw that perlop does not mention that '-' is allowed at the
start. Well, it is mentioned as a special case for unary minus,
but the description of '=>' says it ignores precedence which
suggests that the unary minus special case doesn't apply. And
in toke.c there is another special case for '-bareword =>' which
implies to me that this should be mentioned in the docs for '=>'.

---

---

Flags​:
  category=docs
  severity=low
  Type=Patch
  PatchStatus=HasPatch

---

Site configuration information for perl 5.29.9​:

Configured by fanf2 at Fri Mar 1 16​:47​:41 GMT 2019.

Summary of my perl5 (revision 5 version 29 subversion 9) configuration​:
  Local Commit​: ab9c75bb9b8c06b34fb988bdd5170b0976b38cbb
  Ancestor​: de59f38
  Platform​:
  osname=linux
  osvers=4.9.0-8-amd64
  archname=x86_64-linux
  uname='linux grey.csi.cam.ac.uk 4.9.0-8-amd64 #1 smp debian 4.9.130-2 (2018-10-27) x86_64 gnulinux '
  config_args='-des -Dusedevel'
  hint=recommended
  useposix=true
  d_sigaction=define
  useithreads=undef
  usemultiplicity=undef
  use64bitint=define
  use64bitall=define
  uselongdouble=undef
  usemymalloc=n
  default_inc_excludes_dot=define
  bincompat5005=undef
  Compiler​:
  cc='cc'
  ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
  optimize='-O2'
  cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
  ccversion=''
  gccversion='6.3.0 20170516'
  gccosandvers=''
  intsize=4
  longsize=8
  ptrsize=8
  doublesize=8
  byteorder=12345678
  doublekind=3
  d_longlong=define
  longlongsize=8
  d_longdbl=define
  longdblsize=16
  longdblkind=3
  ivtype='long'
  ivsize=8
  nvtype='double'
  nvsize=8
  Off_t='off_t'
  lseeksize=8
  alignbytes=8
  prototype=define
  Linker and Libraries​:
  ld='cc'
  ldflags =' -fstack-protector-strong -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/6/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib /lib64 /usr/lib64
  libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
  perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
  libc=libc-2.24.so
  so=so
  useshrplib=false
  libperl=libperl.a
  gnulibc_version='2.24'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs
  dlext=so
  d_dlsymun=undef
  ccdlflags='-Wl,-E'
  cccdlflags='-fPIC'
  lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'

Locally applied patches​:
  ab9c75bb9b8c06b34fb988bdd5170b0976b38cbb

---

@​INC for perl 5.29.9​:
  lib
  /usr/local/lib/perl5/site_perl/5.29.9/x86_64-linux
  /usr/local/lib/perl5/site_perl/5.29.9
  /usr/local/lib/perl5/5.29.9/x86_64-linux
  /usr/local/lib/perl5/5.29.9

---

Environment for perl 5.29.9​:
  HOME=/home/fanf2
  LANG (unset)
  LANGUAGE (unset)
  LC_CTYPE=C.UTF-8
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/home/fanf2/bin​:/home/fanf2/gnu/bin​:/opt/bind/bin​:/usr/local/sbin​:/usr/local/bin​:/usr/sbin​:/usr/bin​:/usr/games​:/sbin​:/bin
  PERL_BADLANG (unset)
  SHELL=/bin/bash

[p5pRT]

From dot@dotat.at

0001-perlop-words-before-a-fat-arrow-comma-can-start-with.patch

From ab9c75bb9b8c06b34fb988bdd5170b0976b38cbb Mon Sep 17 00:00:00 2001
Message-Id: <ab9c75bb9b8c06b34fb988bdd5170b0976b38cbb.1551458815.git.dot@dotat.at>
From: Tony Finch <dot@dotat.at>
Date: Fri, 1 Mar 2019 16:42:12 +0000
Subject: [PATCH] perlop: words before a fat arrow comma can start with -

---
 pod/perlop.pod | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pod/perlop.pod b/pod/perlop.pod
index af695b678f..5b6c391b5d 100644
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -1250,7 +1250,7 @@ from left to right.
 The C<< => >> operator (sometimes pronounced "fat comma") is a synonym
 for the comma except that it causes a
 word on its left to be interpreted as a string if it begins with a letter
-or underscore and is composed only of letters, digits and underscores.
+or underscore or minus and is composed only of letters, digits and underscores.
 This includes operands that might otherwise be interpreted as operators,
 constants, single number v-strings or function calls.  If in doubt about
 this behavior, the left operand can be quoted explicitly.
-- 
2.18.0

[p5pRT]

From @jkeenan

On Fri, 01 Mar 2019 17​:39​:21 GMT, dot@​dotat.at wrote​:

This is a bug report for perl from dot@​dotat.at,
generated with the help of perlbug 1.41 running under perl 5.29.9.

-----------------------------------------------------------------

I was checking whether '-' is allowed inside barewords before
fat arrows, as well as at the start of the bareword, and I
saw that perlop does not mention that '-' is allowed at the
start. Well, it is mentioned as a special case for unary minus,
but the description of '=>' says it ignores precedence which
suggests that the unary minus special case doesn't apply. And
in toke.c there is another special case for '-bareword =>' which
implies to me that this should be mentioned in the docs for '=>'.

Could you prepare a patch (probably in pod/perlop.pod) for the change of documentation you would like to see?

(Patches are best prepared in a git checkout of the Perl 5 respository, using 'git format-patch'. However, 'patch' and 'diff' also can be used.)

Thank you very much.
--
James E Keenan (jkeenan@​cpan.org)

[p5pRT]

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

[p5pRT]

From @tonycoz

On Fri, 01 Mar 2019 09​:39​:21 -0800, dot@​dotat.at wrote​:

I was checking whether '-' is allowed inside barewords before
fat arrows, as well as at the start of the bareword, and I
saw that perlop does not mention that '-' is allowed at the
start. Well, it is mentioned as a special case for unary minus,
but the description of '=>' says it ignores precedence which
suggests that the unary minus special case doesn't apply. And
in toke.c there is another special case for '-bareword =>' which
implies to me that this should be mentioned in the docs for '=>'.

The - isn't part of the bareword, the -foo => ... results in the unary negation operator being applied to the foo bareword​:

tony@​mars​:.../git/perl$ ./perl -Dt -e '-foo => 1'
(-e​:1) const(PV("foo"\0))
(-e​:1) negate

EXECUTING...

(-e​:0) enter
(-e​:0) nextstate
(-e​:1) leave

This is documented in perlop​:

Unary C<"-"> performs arithmetic negation if the operand is numeric,
including any string that looks like a number. If the operand is
an identifier, a string consisting of a minus sign concatenated
with the identifier is returned. Otherwise, if the string starts
with a plus or minus, a string starting with the opposite sign is
returned. One effect of these rules is that C<-bareword> is equivalent
to the string C<"-bareword">. If, however, the string begins with a
non-alphabetic character (excluding C<"+"> or C<"-">), Perl will attempt
to convert
the string to a numeric, and the arithmetic negation is performed. If the
string cannot be cleanly converted to a numeric, Perl will give the warning
B<Argument "the string" isn't numeric in negation (-) at ...>.
X<-> X<negation, arithmetic>

Tony

[p5pRT]

From dot@dotat.at

On 3 Mar 2019, at 00​:17, James E Keenan via RT <perlbug-followup@​perl.org> wrote​:

Could you prepare a patch (probably in pod/perlop.pod) for the change of documentation you would like to see?

Yep, done, and attached to the report using perlbug as described in https://perldoc.perl.org/perlhack.html#PATCHING-PERL

Tony.
--
f.anthony.n.finch <dot@​dotat.at> http​://dotat.at

[p5pRT]

From dot@dotat.at

On 3 Mar 2019, at 01​:29, Tony Cook via RT <perlbug-followup@​perl.org> wrote​:

The - isn't part of the bareword, the -foo => ... results in the unary negation operator being applied to the foo bareword​:

Yep, that’s kind of right, and I explained that in my bug report, but the documentation is still incomplete and confusing and does not match the special case for -bareword=> in toke.c. See https://perl5.git.perl.org/perl.git/blob/HEAD:/toke.c#l5666for the code that implements the special case for - before a bareword before =>

This code overrides the bit of the documentation which says barewords before => override all operator precedence. See https://perl5.git.perl.org/perl.git/blob/HEAD:/pod/perlop.pod#l1280

So if I am looking up the syntax for what appears before => in the current docs I need to know that “bareword” is jargon for “interpreted as a string” (but the explanation of => does not mention “bareword”) and I need to know that the explanation for how the - operator works on barewords is not just a property of the operator, but also a property of the lexical syntax that has an undocumented special case before =>

Tony.
--
f.anthony.n.finch <dot@​dotat.at> http​://dotat.at