FAQ
Author: lwall
Date: 2009-02-07 00:27:35 +0100 (Sat, 07 Feb 2009)
New Revision: 25223

Modified:
docs/Perl6/Spec/S02-bits.pod
Log:
refactor pseudo-package names
clarify use of protoobjects as responder to subcall interface


Modified: docs/Perl6/Spec/S02-bits.pod
===================================================================
--- docs/Perl6/Spec/S02-bits.pod 2009-02-06 23:25:26 UTC (rev 25222)
+++ docs/Perl6/Spec/S02-bits.pod 2009-02-06 23:27:35 UTC (rev 25223)
@@ -12,9 +12,9 @@

Maintainer: Larry Wall <larry@wall.org>
Date: 10 Aug 2004
- Last Modified: 1 Feb 2009
+ Last Modified: 6 Feb 2009
Number: 2
- Version: 151
+ Version: 152

This document summarizes Apocalypse 2, which covers small-scale
lexical items and typological issues. (These Synopses also contain
@@ -512,7 +512,7 @@
# and is implemented by the MyScalar class
my Int $x is MyScalar;

-Note that C<$x> is also initialized to C<::Int>. See below for more on this.
+Note that C<$x> is also initialized to the C<Int> protoobject. See below for more on this.

=item *

@@ -525,12 +525,18 @@
$spot.defined; # False
say $spot; # "Dog"

-Any class name used as a value by itself is an undefined instance of
-that class's prototype, or I<protoobject>. See S12 for more on that.
-(Any type name in rvalue context is parsed as a list operator
-indicating a typecast, but an argumentless one of these degenerates
-to a typecast of undef, producing the protoobject.)
+Any type name used as a value is an undefined instance of
+that type's prototype object, or I<protoobject>. See S12 for more on that.
+Any type name in rvalue context is parsed as a single protoobject value and
+expects no arguments following it. However, a protoobject responds to the function
+call interface, so you may use the name of a protoobject with parentheses as if it
+were a function, and any argument supplied to the call is coerced
+to the type indicated by the protoobject. If there is no argument
+in the parentheses, the protoobject returns itself:

+ my $type = Num; # protoobject as a value
+ $num = $type($string) # coerce to Num
+
To get a real C<Dog> object, call a constructor method such as C<new>:

my Dog $spot .= new;
@@ -1760,37 +1766,51 @@

The following pseudo-package names are reserved at the front of a name:

- MY # Lexical symbols declared in the current scope
- OUR # Package symbols declared in the current package
- FILE # Lexical symbols in this file's outermost scope
- PERL # Lexical symbols in the standard setting
- LANG # Lexical symbols in current DSL (usually PERL)
- GLOBAL # Interpreter-wide package symbols
- PROCESS # Process-related globals (superglobals)
- SUPER # Package symbols declared in inherited classes
+ MY # Symbols in the current lexical scope (aka $?SCOPE)
+ OUR # Symbols in the current package (aka $?PACKAGE)
+ CORE # Outermost lexical scope, definition of standard Perl
+ GLOBAL # Interpreter-wide package symbols, really CORE::GLOBAL
+ PROCESS # Process-related globals (superglobals), CORE::PROCESS
COMPILING # Lexical symbols in the scope being compiled
+ CALLER # Contextual symbols in the immediate caller's lexical scope
+ CONTEXT # Contextual symbols in my or any caller's lexical scope

The following relative names are also reserved but may be used
anywhere in a name:

- OUTER # Lexical symbols declared in the outer scope
- CALLER # Contextual symbols in the immediate caller's scope
- CONTEXT # Contextual symbols in any context's scope
+ OUTER # Symbols in the next outer lexical scope
+ UNIT # Symbols in the outermost lexical scope of compilation unit
+ SETTING # Lexical symbols in the unit's DSL (usually CORE)
+ PARENT # Symbols in this package's parent package (or lexical scope)

+The following is reserved at the beginning of method names in method calls:
+
+ SUPER # Package symbols declared in inherited classes
+
Other all-caps names are semi-reserved. We may add more of them in
the future, so you can protect yourself from future collisions by using
mixed case on your top-level packages. (We promise not to break
any existing top-level CPAN package, of course. Except maybe C<ACME>,
and then only for coyotes.)

-The C<LANG> scope is equivalent to C<FILE::OUTER>. For a standard Perl
-program C<LANG> is the same as C<PERL>, but various startup options
-(such as C<-n> or C<-p>) can put you into a domain specific language,
-in which case C<PERL> remains the scope of the standard language,
-while C<LANG> represents the scope defining the DSL that functions
+The file's scope is known as C<UNIT>, but there are one or more
+lexical scopes outside of that corresponding to the linguistic setting
+(often known as the prelude in other cultures). Hence, the C<SETTING>
+scope is equivalent to C<UNIT::OUTER>. For a standard Perl program
+C<SETTING> is the same as C<CORE>, but various startup options (such
+as C<-n> or C<-p>) can put you into a domain specific language,
+in which case C<CORE> remains the scope of the standard language,
+while C<SETTING> represents the scope defining the DSL that functions
as the setting of the current file. See also the C<-L>/C<--language>
switch described in L<S19-commandline>.

+Note that, since the C<UNIT> of an eval is the eval string itself,
+the C<SETTING> of an eval is the language in effect at the point
+of the eval, not the language in effect at the top of the file.
+(You may, however, use C<OUTER::SETTING> to get the setting of the
+code that is executing the eval.) In more traditional terms, the
+normal program is functioning as the "prelude" of the eval.
+
=item *

You may interpolate a string into a package or variable name using
@@ -2077,6 +2097,7 @@
$?VM Which virtual machine am I compiling under
$?XVM Which virtual machine am I cross-compiling for
$?PERL Which Perl am I compiled for?
+ $?SCOPE Which lexical scope am I in?
$?PACKAGE Which package am I in?
@?PACKAGE Which nested packages am I in?
$?MODULE Which module am I in?

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