Author: larry
Date: Wed Jun 11 16:26:27 2008
New Revision: 14548
Modified:
doc/trunk/design/syn/S03.pod
Log:
clarification of reduced short-circuit ops
Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Wed Jun 11 16:26:27 2008
@@ -1203,8 +1203,15 @@
is true. In list context forces a false return to mean C<()>.
See C<xor> below for low-precedence version.
-Similar to the C<[^^]> reduce operator, but short-circuits in the sense
-that it does not evaluate any arguments after a 2nd true result.
+This operator short-circuits in the sense that it does not evaluate
+any arguments after a 2nd true result. Closely related is the reduce
+operator:
+
+ [^^] a(), b(), c() ...
+
+but note that reduce operators are not macros but ordinary list
+operators, so c() is always called before the reduce is done.
+
=item *
@@ -1704,7 +1711,7 @@
[+] [*] [<] [\+] [\*] etc.
-See L<Reduction operators>.
+See L<Reduction operators> below.
=item *
@@ -3486,7 +3493,7 @@
[-] 4, 3, 2; # 4-3-2 = (4-3)-2 = -1
[**] 4, 3, 2; # 4**3**2 = 4**(3**2) = 262144
-For list-associating operators (like C<< < >>), all arguments are taken
+For chain-associative operators (like C<< < >>), all arguments are taken
together, just as if you had written it out explicitly:
[<] 1, 3, 5; # 1 < 3 < 5
@@ -3635,6 +3642,15 @@
(And, in fact, the latter are already easy to express anyway,
and more obviously nonsensical.)
+Similarly, list-associative operators that have the thunk-izing
characteristics of
+macros (such as short-circuit operators) lose those macro-like characteristics.
+You can say
+
+ [||] a(), b(), c(), d()
+
+to return the first true result, but the evaluation of the list is controlled
+by the semantics of the list, not the semantics of C<||>.
+
Most reduce operators return a simple scalar value, and hence do not care
whether they are evaluated in item or list context. However, as with
other list operators and functions, a reduce operator may return a list
