Author: larry
Date: Thu Sep 6 09:31:16 2007
New Revision: 14447
Modified:
doc/trunk/design/syn/S03.pod
Log:
Add logic programming primitives with decent binding of intermediate state
The much-despised "err" operator is gone; use "orelse" instead
Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Thu Sep 6 09:31:16 2007
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 8 Mar 2004
- Last Modified: 30 Aug 2007
+ Last Modified: 6 Aug 2007
Number: 3
- Version: 120
+ Version: 121
=head1 Overview
@@ -48,8 +48,8 @@
Comma operator ,
List infix Z minmax X X~X X*X XeqvX
List prefix = : print push say die map substr ... [+] [*] any $ @
- Loose and and
- Loose or or xor err
+ Loose and and andthen
+ Loose or or xor orelse
Terminator ; <==, ==>, <<==, ==>>, {...}, modifiers, extra ), ], }
If you don't see your favorite operator there, the following
@@ -59,7 +59,7 @@
=head2 Term precedence
This isn't really a precedence level, but it's in here because no operator
-can have tighter precedence than a term. See S02 for longer descriptions of
+can have tighter precedence than a term. See S03 for longer descriptions of
various terms.
=over
@@ -1008,13 +1008,14 @@
=item *
-C<< infix:<//> >>, defined-or
+C<< infix:<//> >>, default operator
$value // $default
Returns the left argument if it's defined, otherwise evaluates and
returns the right argument. In list context forces a false return
-to mean C<()>. See C<err> below for low-precedence version.
+to mean C<()>. See C<orelse> below for a similar but not identical
+low-precedence version.
=item *
@@ -1497,6 +1498,30 @@
a false return to mean C<()>. See C<&&> above for high-precedence
version.
+=item *
+
+C<< infix:<andthen> >>, proceed on success
+
+ test1() andthen test2()
+
+Returns the left argument if the left argument indicates failure
+(that is, if the result is undefined). Otherwise it
+evaluates and returns the right argument.
+
+If the right side is a block or pointy block, the result of the left
+side is bound to any arguments of the block. If the right side is
+not a block, a block scope is assumed around the right side, and the
+result of the left side is implicitly bound to C<$_> for the scope
+of the right side. That is,
+
+ test1() andthen test2()
+
+is equivalent to
+
+ test1() andthen -> $_ { test2() }
+
+There is no corresponding high-precedence version.
+
=back
=head2 Loose or precedence
@@ -1526,13 +1551,28 @@
=item *
-C<< infix:<err> >>, short-circuit defined-or
+C<< infix:<orelse> >>, proceed on failure
- $value err $default
+ test1() orelse test2()
-Returns the left argument if it's defined, otherwise evaluates and
-returns the right argument. In list context forces a false return
-to mean C<()>. See C<//> above for high-precedence version.
+Returns the left argument if the left argument indicates success
+(that is, if the result is defined). Otherwise it evaluates and
+returns the right argument.
+
+If the right side is a block or pointy block, the result of the left
+side is bound to any arguments of the block. If the right side is
+not a block, a block scope is assumed around the right side, and the
+result of the left side is implicitly bound to C<$!> for the scope
+of the right side. That is,
+
+ test1() orelse test2()
+
+is equivalent to
+
+ test1() orelse -> $! { test2() }
+
+(The low-precedence C<//> operator is similar, but does not set C<$!> or
+treat blocks specially.)
=back
