[svn:perl6-synopsis] r14595 - doc/trunk/design/syn
la...@cvs.perl.org
Date: Tue Oct 14 17:14:18 2008
New Revision: 14595
Modified:
doc/trunk/design/syn/S02.pod
doc/trunk/design/syn/S04.pod
doc/trunk/design/syn/S06.pod
doc/trunk/design/syn/S09.pod
doc/trunk/design/syn/S12.pod
Log:
delete ambiguous use of {...} for hash unpacking, just use sigs for that
(list unpacking may still be done with [...] for clarity)
simplify parsing of expressions in conditionals to dwim on map/grep blocks
(you now need to parenthesize only on listops called with 0 args, like caller)
define .pick on enumerable types, e.g. Day.pick
clean out old instances of rand ARG, esp. where used as example of 0-or-1-ary
revamp obsolete usages of exists
Modified: doc/trunk/design/syn/S02.pod
==============================================================================
--- doc/trunk/design/syn/S02.pod (original)
+++ doc/trunk/design/syn/S02.pod Tue Oct 14 17:14:18 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <la...@wall.org>
Date: 10 Aug 2004
- Last Modified: 9 Oct 2008
+ Last Modified: 14 Oct 2008
Number: 2
- Version: 138
+ Version: 139
This document summarizes Apocalypse 2, which covers small-scale
lexical items and typological issues. (These Synopses also contain
@@ -1096,8 +1096,8 @@
# Anything assigned to the variable $mitsy must conform
# to the type Fish and either the Cat or Dog type...
- my Cat|Dog Fish $mitsy = new Fish but { int rand 2 ?? .does Cat
- !! .does Dog };
+ my Cat|Dog Fish $mitsy = new Fish but { Bool.pick ?? .does Cat
+ !! .does Dog };
=head2 Parameter types
Modified: doc/trunk/design/syn/S04.pod
==============================================================================
--- doc/trunk/design/syn/S04.pod (original)
+++ doc/trunk/design/syn/S04.pod Tue Oct 14 17:14:18 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <la...@wall.org>
Date: 19 Aug 2004
- Last Modified: 1 Sep 2008
+ Last Modified: 14 Oct 2008
Number: 4
- Version: 69
+ Version: 70
This document summarizes Apocalypse 4, which covers the block and
statement syntax of Perl.
@@ -1080,11 +1080,11 @@
}
parentheses aren't necessary around C<EXPR> because the whitespace
-between C<EXPR> and the block forces the block to be considered a
-block rather than a subscript. This works for all control structures,
-not just the new ones in Perl 6. A top-level bare block
-is always considered a statement block if there's space
-before it:
+between C<EXPR> and the block forces the block to be considered a block
+rather than a subscript, provided the block occurs where an infix
+operator would be expected. This works for all control structures,
+not just the new ones in Perl 6. A top-level bare block is always
+considered a statement block if there's a term and a space before it:
if $foo { ... }
elsif $bar { ... }
@@ -1094,30 +1094,24 @@
You can still parenthesize the expression argument for old times'
sake, as long as there's a space between the closing paren and the
-opening brace. You I<must> parenthesize the expression if there is
-a bare block or pointy block that would be misinterpreted as the statement's
-block. This is regardless of whether a term or operator is expected where
-the block occurs. (A block inside brackets, or used as a
-postcircumfix is fine, though.) Any block with whitespace
-in front of it will be taken as terminating the conditional, even if
-the conditional expression could take another argument. Therefore
-
- if rand { say "exists" } { extra() }
- if rand -> $x { say "exists" } { extra() }
-
-is always parsed as
-
- if (rand) { say "exists" }; { extra() }
- if (rand) -> $x { say "exists" }; { extra() }
-
-rather than
-
- if (rand { say "exists" }) { extra() }
- if (rand (-> $x { say "exists" })) { extra() }
-
-Apart from that, it is illegal to use a bare closure where an
-operator is expected. (Remove the whitespace if you wish it to be
-a postcircumfix.)
+opening brace. (Otherwise it will be parsed as a hash subscript.)
+
+Note that the parser cannot intuit how many arguments a list operator
+is taking, so if you mean 0 arguments, you must parenthesize the
+argument list to force the block to appear after a term:
+
+ if caller {...} # WRONG, parsed as caller({...})
+ if caller() {...} # okay
+ if (caller) {...} # okay
+
+Note that common idioms work as expected though:
+
+ for map { $^a + 1 }, @list { .say }
+
+Unless you are parsing a statement that expects a block argument,
+it is illegal to use a bare closure where an operator is expected
+because it will be considered to be two terms in row.
+(Remove the whitespace if you wish it to be a postcircumfix.)
Anywhere a term is expected, a block is taken to be a closure definition
(an anonymous subroutine). If the closure is empty, or appears to contain
Modified: doc/trunk/design/syn/S06.pod
==============================================================================
--- doc/trunk/design/syn/S06.pod (original)
+++ doc/trunk/design/syn/S06.pod Tue Oct 14 17:14:18 2008
@@ -13,9 +13,9 @@
Maintainer: Larry Wall <la...@wall.org>
Date: 21 Mar 2003
- Last Modified: 11 Oct 2008
+ Last Modified: 14 Oct 2008
Number: 6
- Version: 95
+ Version: 96
This document summarizes Apocalypse 6, which covers subroutines and the
@@ -713,10 +713,8 @@
undefined is not considered to be missing, and hence does not trigger
the default. Use C<//=> within the body for that.)
-(Conjectural: Within the body you may also use C<exists> on the
-parameter name to determine whether it was passed. Maybe this will have to
-be restricted to the C<?> form, unless we're willing to admit that a parameter
-could be simultaneously defined and non-existent.)
+You may check whether an optional parameter was bound to anything
+by calling C<VAR($param).defined>.
=head2 Named parameters
@@ -1356,39 +1354,9 @@
sub quicksort (:$reverse, :$inplace, *$pivot, *@data)
-=head2 Unpacking hash parameters
-
-Likewise, a hash argument can be mapped to a hash of parameters, specified
-as named parameters within curlies. Instead of saying:
-
- sub register (%guest_data, $room_num) {
- my $name := delete %guest_data<name>;
- my $addr := delete %guest_data<addr>;
- ...
- }
-
-you can get the same effect with:
-
- sub register ({:$name, :$addr, *%guest_data}, $room_num) {
- ...
- }
-
-Use of the curly form is not allowed where it might be confused with the
-following block's opening curly:
-
- -> {:$name, :$addr, *%guest_data}, $room_num { # WRONG
-
-However, as described in the next section, you can always use a
-sub-signature instead:
-
- -> (:$name, :$addr, *%guest_data), $room_num { # note ()'s
-
-In fact, the [...] and {...} forms are really just extra documentation
-about what you expect.
-
=head2 Unpacking tree node parameters
-You can unpack tree nodes in various dwimmy ways by enclosing the bindings
+You can unpack hash values and tree nodes in various dwimmy ways by enclosing the bindings
of child nodes and attributes in parentheses following the declaration of
the node itself:
Modified: doc/trunk/design/syn/S09.pod
==============================================================================
--- doc/trunk/design/syn/S09.pod (original)
+++ doc/trunk/design/syn/S09.pod Tue Oct 14 17:14:18 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <la...@wall.org>
Date: 13 Sep 2004
- Last Modified: 17 July 2008
+ Last Modified: 14 Oct 2008
Number: 9
- Version: 28
+ Version: 29
=head1 Overview
@@ -362,7 +362,7 @@
@@x <== %hash.keys.grep: {/^\d+$/};
@@x <== =<>;
@@x <== 1..*;
- @@x <== gather { loop { take rand 100 } };
+ @@x <== gather { loop { take 100.rand } };
@array{@@x}
@@ -374,7 +374,7 @@
@x <== %hash.keys.grep: {/^\d+$/};
@x <== =<>;
@x <== 1..*;
- @x <== gather { loop { take rand 100 } };
+ @x <== gather { loop { take 100.rand } };
@array{@@x} # multidimensional
@array{@x} # flattened
@@ -1206,7 +1206,7 @@
In Perl 6 these read-only operations are indeed non-destructive:
my %hash;
- exists %hash<foo><bar>; # %hash is still empty
+ %hash<foo><bar> :exists; # %hash is still empty
But these bindings I<do> autovivify:
Modified: doc/trunk/design/syn/S12.pod
==============================================================================
--- doc/trunk/design/syn/S12.pod (original)
+++ doc/trunk/design/syn/S12.pod Tue Oct 14 17:14:18 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <la...@wall.org>
Date: 27 Oct 2004
- Last Modified: 21 Aug 2008
+ Last Modified: 14 Oct 2008
Number: 12
- Version: 63
+ Version: 64
=head1 Overview
@@ -1787,6 +1787,26 @@
type C<bit>. Never compare a value to "C<true>", or even "C<True>".
Just use it in a boolean context.
+Enum types (and perhaps certain other finite, enumerable types such
+as finite ranges) define a C<.pick> method on the protoobject of
+that type. Hence:
+
+ my enum CoinFace <Heads Tails>;
+ CoinFace.pick
+
+returns C<Heads> or C<Tails> with equal probability, and
+
+ Month.pick(*)
+
+will return the months in random order. Presumably
+
+ StandardPlayingCards.pick(5)
+
+might return a Royal Flush, but a Full House is much
+more likely. It can never return Five Aces, since the pick
+is done without replacement. (If it I<does> return Five Aces,
+it's time to walk away.)
+
=head1 Open vs Closed Classes
By default, all classes in Perl are non-final, which means