
=head1 TITLE

 [DRAFT] Synopsis 28 - Special Names [DRAFT]

=head1 AUTHORS

    Larry Wall <larry@wall.org>
    Tim Nelson <wayland@wayland.id.au>
    Lyle Hopkins <webmaster@cosmicperl.com>

=head1 VERSION

    Created: 23 Feb 2009, created by Tim Nelson from miscellaneous documents lying around

    Last Modified: 19 Apr 2009
    Version: 6

=head1 Special Variables

=head2 Introduction

This document serves as a collection point
for what is known about special variables
in Perl 6 and correlates them with the changes from Perl 5.

If you are trying to find the Perl 6 equivalent of a Perl 5 special
variable you know, try searching this file for the Perl 5 version.
Each main entry is followed by a note containing the corresponding
Perl 5 variable(s). The list of main entries is also followed by
a table showing the 5 and 6 variables side-by-side.

=head2 Overview

=head3 Secondary Sigils (also known as "twigils")

A quick reminder of the relevant twigils from S02:

    $?foo   # Compiler constants (fixed at compile time)
    $*foo   # Context variable, default global (run time)
    $=foo   # File-scoped POD data

The various C<$?foo> variables are determined at compile time, and are
not modifiable at run time.  This does not mean that the variable has the
same value everywhere; for instance, C<$?LINE> is different on every line
of the program.

The C<$*foo> variables function both as dymamically scoped variables
and as globals.  Globalness is relative, in other words.  Any dynamic
scope may modify the set of globals visible via the C<$*foo> notation.
Most of the standard globals listed below actually live either in
the C<PROCESS> or the C<GLOBAL> package, where C<PROCESS> contains
globals belonging to the entire process, while C<GLOBAL> contains the
globals belonging to the current interpreter, since a process may be
running more than one interpreter.  Unless otherwise indicated below,
the outermost definition of these variables are kept in the C<PROCESS>
package.

The C<$=foo> variables are related to the C<$?foo> variables
insofar as the text of the program is known at compile time, so the
values are static.  However, the different twigil indicates that the
variable contains POD data, which is primarily under user control
rather than compiler control.  The structure of these variables will
be fleshed out in S26.

=head3 Named variables

 Variable          Spec  Type         Description
 --------          ----  ----         -----------

 @_                                   # ???
 $!                S04                # Current Exception object
 $/                S05   Match        # Last match
 $0, $1, $2        S05   Str          # First captured value from match: $/[0]
 $?ARCH                  SoftwarePackage # Host architecture
 $?XARCH                 SoftwarePackage # Target architecture
 @*ARGS            S06   Array of Str # command-line arguments
 $*ARGFILES        S02   IO           # The magic command-line input handle
 &?BLOCK           S06   Block        # current block (itself)
 ::?CLASS          S12   Str          # current class (as package or type name)
 $?CLASS           S02   Class        # current class
 @=COMMENT        (S26)               # All the comment blocks in the file
 %?CONFIG                Hash of XXX  # configuration hash XXX What does this do?
 $*CWD                   Str          # current working directory
 $=DATA           (S26)  IO           # data block handle (=begin DATA ... =end)
 @=DATA           (S26)  Array        # Same as above, but array
 %?DEEPMAGIC       S13   Hash of XXX  # Controls the mappings of magical names to sub definitions
 $?DISTRO          S02   SoftwarePackage # Which OS distribution am I compiling under
 $*DISTRO          S02   SoftwarePackage # Which OS distribution am I running under
 $*EGID                  Int          # effective group id
 %*ENV             S02   Hash of Str  # system environment variables
 $*ERR             S16   IO           # Standard error handle
 $*EUID                  Int          # effective user id
 $*EXECUTABLE_NAME       Str          # executable name
 $?FILE            S02   Str          # current filename of source file
 $?GRAMMAR         S02   Grammar      # current grammar
 $*GID                   Int          # group id
 $*IN              S16   IO           # Standard input handle; is an IO object
 @*INC             S11                # where to search for user modules (but not std lib!)
 %?LANG            S02   Hash of Grammar # What is the current set of interwoven languages?
 $*LANG            S02   Str          # LANG variable from %*ENV that defines what human language is used
 $?LINE            S02   Int          # current line number in source file
 %*META-ARGS       S19   Hash of XXX  # Meta-arguments
 $?MODULE          S02   Module       # current module
 %*OPTS            S19   Hash of XXX  # Options from command line
 %*OPT...          S19   Hash of XXX  # Options from command line to be passed down
 $?KERNEL                SoftwarePackage # operating system compiled for
 $*KERNEL                SoftwarePackage # operating system running under
 $*OUT             S16   IO           # Standard output handle
 $?PACKAGE         S02   Package      # current package
 $?PERL            S02   SoftwarePackage # Which Perl am I compiled for?
 $*PERL            S02   SoftwarePackage # perl version running under
 $*PID                   Int          # system process id
 %=POD             S02                # (or some such)
 $*PROGRAM_NAME    S19   Str          # name of the Perl program being executed
 %*PROTOCOLS       S16   Hash of Method # Stores the methods needed for the uri() function
 ::?ROLE                 Str          # current role (as package or type name)
 $?ROLE            S02   Role         # current role
 &?ROUTINE         S06   Routine      # current sub or method (itself)
 $?SCOPE           S02                # Current "my" scope (XXX unnecessary?)
 $*UID                   Int          # system user id
 $?USAGE           S06   Str          # Default usage message generated at compile time
 $?VM              S02   SoftwarePackage # Which virtual machine am I compiling under
 $?XVM             S02   SoftwarePackage # Which virtual machine am I cross-compiling for

Note that contextual variables such as C<$*OUT> may have more than
one current definition in the outer dynamic context, in which case
the innermost dynamic scope determines the meaning.  For instance,
C<$PROCESS::OUT> is the stdout for the entire process, but each
interpreter can set its own C<$GLOBAL::OUT> to make C<$*OUT> mean
whatever it wants independently of other interpreters.  Any dynamic
scope may also declare a local meaning of C<$*OUT> that applies only
to called code.  Likewise each thread could log its own errors
to its own C<$*ERR>, since a thread is a dynamic scope.

=head2 Special Classes

These are classes defined especially for the benefit of the Special Variables.

 class SoftwarePackage {
     has Str $name;
     has Version $version;
 }

This class is intended to represent a software package at a fairly basic level.

=head3 Perl5 to Perl6 special variable translation

If a column has a "-" in it, it means that item is unavailable in that version of Perl.

 Perl 5              Perl 6         Comment
 -----------         -----------    -----------------------
 STDIN               $*IN           See S16; actual variable is $PROCESS::IN
 STDOUT              $*OUT          See S16; actual variable is $PROCESS::OUT
 STDERR              $*ERR          See S16; actual variable is $PROCESS::ERR
 $_ $ARG             $_             More lexically aware
 $_[1],$_[2]..       $^a,$^b..
 $a,$b               -              Just params to anonymous block
 -                   $/             Object with results of last regex match
 $1,$2,$3...         $1,$2,$3...
 $& $MATCH           $<>
 $` $PREMATCH        substr based on $/.from
 $' $POSTMATCH       substr based on $/.to
 $+                  -              But info can now be retrieved from $/
 $^N                 $*MOST_RECENT_CAPTURED_MATCH  ...or some such.
                       or $/[*-$n]                       ...or omit
 @-                  $1.start, etc
 @+                  $1.end, etc.
 %!                  -
 $[                  -              This feature has been removed
 $*                  -              Deprecated long ago
 $#                  -              Deprecated long ago
 $^H                 -              These were only ever internal anyway
 %^H                 -
 -                   $!             Current exception (see L<S04-control>)
 $! $ERRNO $OS_ERROR -              Use shiny new $!
 $?  $CHILD_ERROR    -              Use shiny new $!
 $@  $EVAL_ERROR     -              Use shiny new $!
 $^E                 -              Use shiny new $!
 $^S                 -
 $. $NR              $*IN.input_record_number()
 $/ $RS              $*IN.input_record_separator()
 $|                  $*OUT.autoflush()
 $, $OFS             $*OUT.output_field_separator()
 $\                  $*OUT.output_record_separator()
 $" $LIST_SEPARATOR  -
 $; $SUBSEP          -
 $$ $PID             $*PID
 $< $UID             $*UID          Real UID (User ID)
 $( $GID             $*GID          Real GID (Group ID)
 $> $EUID            $*EUID         Effective UID
 $) $EGID            $*EGID         Effective GID
 $0 $PROGRAM_NAME    $*PROGRAM_NAME
 $^C $COMPILING      $*COMPILING
 $^D $DEBUGGING      $*DEBUGGING
 $^F $SYS_FD_MAX     $*SYS_FD_MAX   ...or some such
 $^I $INPLACE_EDIT   $*INPLACE_EDIT ...or some such
 $^M                 $*EMERGENCY_MEMORY ...or some such (or omit)
 $^O $OSNAME         $*OSNAME       ...or some such
 $^P $PERLDB         $*PERLDB       ...or some such
 $^R                 $*LAST_REGEXP_CODE_RESULT   ...or some such. Or omit.
 $^T $BASETIME       $*INITTIME     A Temporal::Instant object
 $^V $]              $?PERL.version
 $^W                 $*WARNINGS (if any dynamic control needed)
 ${^WARNING_BITS}    $?WARNINGS
 $^X                 $*EXECUTABLE_NAME ...or some such
 ARGV                $*ARGFILE      Note the P6 idiom for this handle:
                                    for lines() {
                                      # each time through loop
                                      # proc a line from files named in ARGS
                                    }
 @ARGV               @*ARGS
 ARGVOUT             TBD
 $ARGV               TBD
 @F                  @_
 %ENV                %*ENV
 @INC                @*INC (but not for std library modules)
 %INC                %*INC (maybe, if needed)
 %SIG                event filters plus exception translation
 $SIG{__WARN__}      $*ON_WARN
 $SIG{__DIE__}       $*ON_DIE
 ${^OPEN}            -              This was internal; forget it

=head2 NOT YET DEFINED

The following items are not yet defined, but will need to be defined.

XXX Don't remove this line until this section is completely blank.

We also seem to have $*INC in the table at the top, @*INC in S19 and the table
immediately above, %*INC also in the table above.

The $?LANG and $*LANG variables are also confusing (both in S02).

=head3 Form.pm

These go in the Perl5 to Perl6 conversion table:

 Perl6   Perl5
 -----   -----------------------------------------
 -       $%  $FORMAT_PAGE_NUMBER
 -           HANDLE->format_page_number(EXPR)

 -       $=  $FORMAT_LINES_PER_PAGE
 -           HANDLE->format_lines_per_page(EXPR)

 -       $-  $FORMAT_LINES_LEFT
 -           HANDLE->format_lines_left(EXPR)

 -       $~  $FORMAT_NAME
 -           HANDLE->format_name(EXPR)

 -       $^  $FORMAT_TOP_NAME
 -           HANDLE->format_top_name(EXPR)

 -       $:  $FORMAT_LINE_BREAK_CHARACTERS
 -           IO::Handle->format_line_break_characters

 -       $^L $FORMAT_FORMFEED
 -           IO::Handle->format_formfeed

 -       $^A $ACCUMULATOR

=head3 S15-unicode.pod

${^ENCODING} variable -- S32/Str.pod implies this is $?ENC
$?NF -- unicode normalisation form
${^UNICODE} variable

=head3 Infectious trait spec

${^TAINT} variable, which is pending, among other things, infectious trait spec

=head1 Additions

Please post errors and feedback to perl6-language.  If you are making
a general laundry list, please separate messages by topic.

=for vim:set expandtab sw=4:
