Author: larry
Date: Wed Jan 2 11:30:16 2008
New Revision: 14478
Modified:
doc/trunk/design/syn/S03.pod
doc/trunk/design/syn/S06.pod
Log:
Rationalize migration strategy from Perl 5 to Perl 6 using transitional p5=>
operator
Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Wed Jan 2 11:30:16 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 8 Mar 2004
- Last Modified: 31 Dec 2007
+ Last Modified: 2 Jan 2008
Number: 3
- Version: 125
+ Version: 126
=head1 Overview
@@ -48,7 +48,7 @@
Conditional ?? !! ff fff
Item assignment = := ::= => += -= **= xx= .=
Loose unary true not
- Comma operator ,
+ Comma operator , p5=>
List infix Z minmax X X~X X*X XeqvX
List prefix = : print push say die map substr ... [+] [*] any $ @
Loose and and andthen
@@ -1346,6 +1346,28 @@
Unlike in Perl 5, comma operator never returns the last value. (In item
context it returns a list instead.)
+=item *
+
+C<< infix:«p5=>» >>, the Perl 5 fatarrow
+
+This operator, which behaves exactly like the Perl 5 fatarrow in being
+equivalent to a comma, is purely for easier migration from Perl 5
+to Perl 6. It is not intended for use by programmers in fresh code;
+it is for use by the p5-to-p6 translator to preserve Perl 5 argument
+passing semantics without losing the intent of the notation.
+
+This operator is purposefully ugly and easy to search for. Note that,
+since the operator is equivalent to a comma, arguments come in as
+positional pairs rather than named arguments. Hence, if you have
+a Perl 5 sub that manually handles named argument processing by
+assigning to a hash, it will continue to work. If, however, you edit
+the C<< p5=> >> operator in an argument list to Perl 6's C<< => >>
+operator, it becomes a real named argument, so you must also change
+the called sub to handle real named args, since the named pair will no
+longer come in via C<@_>. You can either name your formal parameters
+explicitly if there is an explicit signature, or pull them out of C<%_>
+rather than C<@_> if there is no explicit signature.
+
=back
=head2 List infix precedence
Modified: doc/trunk/design/syn/S06.pod
==============================================================================
--- doc/trunk/design/syn/S06.pod (original)
+++ doc/trunk/design/syn/S06.pod Wed Jan 2 11:30:16 2008
@@ -13,9 +13,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 21 Mar 2003
- Last Modified: 26 Oct 2007
+ Last Modified: 2 Jan 2008
Number: 6
- Version: 90
+ Version: 91
This document summarizes Apocalypse 6, which covers subroutines and the
@@ -124,18 +124,37 @@
sub foo {...}
-Arguments implicitly come in via the C<@_> array, but they are C<readonly>
-aliases to actual arguments:
+This is equivalent to
- sub say { print qq{"@_[]"\n}; } # args appear in @_
+ sub foo ([EMAIL PROTECTED], *%_) {...}
- sub cap { $_ = uc $_ for @_ } # Error: elements of @_ are read-only
+Positional arguments implicitly come in via the C<@_> array, but
+unlike in Perl 5 they are C<readonly> aliases to actual arguments:
-If you need to modify the elements of C<@_>, declare the array explicitly
-with the C<is rw> trait:
+ sub say { print qq{"@_[]"\n}; } # args appear in @_
- sub swap ([EMAIL PROTECTED] is rw) { @_[0,1] = @_[1,0] }
+ sub cap { $_ = uc $_ for @_ } # Error: elements of @_ are read-only
+Also unlike in Perl 5, Perl 6 has true named arguments, which come in
+via C<%_> instead of C<@_>. (To construct pseudo-named arguments that
+come in via C<@_> as in Perl 5, the p5-to-p6 translator will use the ugly
+C<< p5=> >> operator instead of Perl 6's C<< => >> Pair constructor.)
+
+If you need to modify the elements of C<@_> or C<%_>, declare the
+array or hash explicitly with the C<is rw> trait:
+
+ sub swap ([EMAIL PROTECTED] is rw, *%_ is rw) { @_[0,1] = @_[1,0];
%_<status> = "Q:S"; }
+
+Note: the "rw" container trait is automatically distributed to the
+individual elements by the the slurpy star even though there's no
+actual array or hash passed in. More precisely, the slurpy star
+means the declared formal parameter is I<not> considered readonly; only
+its elements are. See L</Parameters and arguments> below.
+
+Note also that if the sub's block contains placeholder variables (such
+as C<$^foo>), it is considered to have a formal signature already, so
+no implicit bindings to C<@_> or C<%_> are assumed (nor is an explicit
+signature allowed.) So in that case, this section does not apply.
=head2 Blocks
