Author: larry
Date: Fri Aug 25 12:28:00 2006
New Revision: 11421
Modified:
doc/trunk/design/syn/S06.pod
Log:
Discussed relationship of "is" syntax to adverb syntax and type syntax.
Nailed down some (hopefully) sane default behaviors for equiv and assoc.
Modified: doc/trunk/design/syn/S06.pod
==============================================================================
--- doc/trunk/design/syn/S06.pod (original)
+++ doc/trunk/design/syn/S06.pod Fri Aug 25 12:28:00 2006
@@ -13,9 +13,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 21 Mar 2003
- Last Modified: 18 Aug 2006
+ Last Modified: 25 Aug 2006
Number: 6
- Version: 52
+ Version: 53
This document summarizes Apocalypse 6, which covers subroutines and the
@@ -590,7 +590,7 @@
(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-existant.)
+could be simultaneously defined and non-existent.)
=head2 Named parameters
@@ -1663,7 +1663,14 @@
=head2 Subroutine traits
These traits may be declared on the subroutine as a whole (individual
-parameters take other traits).
+parameters take other traits). Trait syntax depends on the particular
+auxiliary you use, but for C<is>, the subsequent syntax is identical to
+adverbial syntax, except that that colon may be omitted or doubled depending
+on the degree of ambiguity desired:
+
+ is ::Foo[...] # definitely a parameterized typename
+ is :Foo[...] # definitely a pair with a list
+ is Foo[...] # depends on whether Foo is predeclared as type
=over
@@ -1707,28 +1714,80 @@
=item C<is tighter>/C<is looser>/C<is equiv>
Specifies the precedence of an operator relative to an existing
-operator. C<equiv> also specifies the default associativity to
-be the same as the operator to which the new operator is equivalent.
-C<tighter> and C<looser> operators default to being left associative.
+operator. C<tighter> and C<looser> operators default to being left
+associative.
+
+C<equiv> on the other hand also clones other traits, so it specifies
+the default associativity to be the same as the operator to which
+the new operator is equivalent. The following are the default
+equivalents for various syntactic categories if neither C<equiv> nor
+C<assoc> is specified. (Many of these have no need of precedence
+or associativity because they are parsed specially. Nevertheless,
+C<equiv> may be useful for cloning other traits of these operators.)
+
+ term:<*>
+ quote:<q>
+ prefix:<++>
+ infix:<+>
+ postfix:<++>
+ circumfix:<( )>
+ postcircumfix:<( )>
+ regex_metachar:<.>
+ regex_backslash:<w>
+ regex_assertion:<?>
+ regex_mod_internal:<i>
+ regex_mod_external:<i>
+ trait_verb:<of>
+ trait_auxiliary:<is>
+ scope_declarator:<my>
+ statement_control:<if>
+ statement_modifier:<if>
+ infix_prefix_meta_operator:<!>
+ infix_postfix_meta_operator:<=>
+ postfix_prefix_meta_operator:{'»'}
+ prefix_postfix_meta_operator:{'«'}
+ infix_circumfix_meta_operator:{'»','«'}
+ prefix_circumfix_meta_operator:{'[',']'}
+
+The existing operator may be specified either as a function name
+or as a string slice equivalent to the one that would be used in
+the complete function name. In string slice form the syntactic
+category will be assumed to be the same as the new declaration.
+Therefore these all have the same effect:
+
+ sub postfix:<!> ($x) is equiv(&postfix:<++>) {...}
+ sub postfix:<!> ($x) is equiv<++> {...}
+ sub postfix:<!> ($x) {...} # since equiv<++> is the default
+
+Prefix operators that are identifiers are handled specially. Both of
+
+ sub foo ($) {...}
+ sub prefix:<foo> ($) {...}
+
+default to named unary precedence despite declaring a prefix operator.
+Likewise postfix operators that look like method calls are forced to
+default to the precedence of method calls.
=item C<is assoc>
Specifies the associativity of an operator explicitly. Valid values are:
- Tag Examples Meaning of $a op $b op $c
- === ======== =========================
- left + - * / x ($a op $b) op $c
- right ** = $a op ($b op $c)
- non cmp <=> .. ILLEGAL
- chain == eq ~~ ($a op $b) and ($b op $c)
- list | & ^ ¥ listop($a, $b, $c) or listop($a; $b; $c)
-
+ Tag Examples Meaning of $a op $b op $c Default
equiv
+ === ======== =========================
=============
+ left + - * / x ($a op $b) op $c +
+ right ** = $a op ($b op $c) **
+ non cmp <=> .. ILLEGAL cmp
+ chain == eq ~~ ($a op $b) and ($b op $c) eqv
+ list | & ^ ¥ op($a, $b, $c) |
Note that operators "C<equiv>" to relationals are automatically considered
chaining operators. When creating a new precedence level, the chaining
-is determined by the presence or absence of "C<is assoc('chain')>",
+is determined by the presence or absence of "C<< is assoc<chain> >>",
and other operators defined at that level are required to be the same.
+Specifying an C<assoc> without an explicit C<equiv> substitutes a default
+C<equiv> consistent with the associativity, as shown in the final column above.
+
=item C<PRE>/C<POST>
Mark blocks that are to be unconditionally executed before/after
