Author: lwall
Date: 2010-02-13 18:41:31 +0100 (Sat, 13 Feb 2010)
New Revision: 29710
Modified:
docs/Perl6/Spec/S02-bits.pod
Log:
[S02] attempt clarification of <a b> semantics wrt parcels and assignment,
jnthn++
Modified: docs/Perl6/Spec/S02-bits.pod
===================================================================
--- docs/Perl6/Spec/S02-bits.pod 2010-02-13 16:15:26 UTC (rev 29709)
+++ docs/Perl6/Spec/S02-bits.pod 2010-02-13 17:41:31 UTC (rev 29710)
@@ -13,8 +13,8 @@
Created: 10 Aug 2004
- Last Modified: 1 Feb 2009
- Version: 198
+ Last Modified: 13 Feb 2009
+ Version: 199
This document summarizes Apocalypse 2, which covers small-scale
lexical items and typological issues. (These Synopses also contain
@@ -2908,7 +2908,7 @@
When used as a subscript it performs a slice equivalent to C<{'foo','bar'}>.
Elsewhere it is equivalent to a parenthesized list of strings:
C<< ('foo','bar') >>. Since parentheses are generally reserved just for
-precedence grouping, they merely autointerpolate in list context. Therefore
+precedence grouping, they merely autointerpolate in flat list context.
Therefore
@a = 1, < x y >, 2;
@@ -2920,7 +2920,7 @@
@a = 1, 'x', 'y', 2;
-In item context, though, the implied parentheses are not removed, so
+In item context, the implied grouping parentheses are still there, so
$a = < a b >;
@@ -2928,26 +2928,41 @@
$a = ('a', 'b');
-which, because the list is assigned to a scalar, is autopromoted into
-a C<Capture> object:
+which, because the parcel is assigned to a scalar, is mostly-eagerly evaluated
as a flat list and
+turned into a C<Seq> object. On the other hand, if you backslash the parcel:
+ $a = \<a b>;
+
+it is like:
+
$a = \('a', 'b');
-Likewise, if bound to a scalar parameter, C<< <a b> >> will be
-treated as a single C<Capture> object, but if bound to a slurpy parameter,
-it will auto-flatten.
+and ends up as a non-flattening object (C<Scalar[Parcel]> or some such).
+Binding is different from assignment. If bound to a signature, the
+C<< <a b> >> parcel will be promoted to a C<Capture> object, but if
+bound to a parameter, it will make the flattening/slicing decision
+based on the nature of the individual parameter. That is, if you
+pass C<< <a b> >> as an argument, it will bind as a single positional
+or slice item, but two slurpy items.
+
But note that under the parenthesis-rewrite rule, a single value will
-still act like a scalar value. These are all the same:
+still act like a single value. These are all the same:
$a = < a >;
$a = ('a');
$a = 'a';
-And if bound to a scalar parameter, no list is constructed.
-To force a single value to become a list object in item context,
-you should use C<< ['a'] >> for clarity as well as correctness.
+That is, a C<Parcel> is actually constructed by the comma, not by
+the parens. To force a single value to become a composite object in
+item context, either add a comma inside parens, or use an appropriate
+constructor or composer for clarity as well as correctness:
+ $a = (< a >,);
+ $a = ('a',);
+ $a = Parcel.new('a');
+ $a = ['a'];
+
For any item in the list that appears to be numeric, the literal is
stored as an object with both a string and a numeric nature, where
the string nature always returns the original string. It is as if
