Author: larry
Date: Sat Dec 23 12:10:42 2006
New Revision: 13500


Clarification on which forms of infix:<~~> are provided dynamically if
    compile-time recognition fails over to multiple dispatch.
Clarification on limits to metaoperator size.

Modified: doc/trunk/design/syn/S03.pod
--- doc/trunk/design/syn/S03.pod        (original)
+++ doc/trunk/design/syn/S03.pod        Sat Dec 23 12:10:42 2006
@@ -14,7 +14,7 @@
   Date: 8 Mar 2004
   Last Modified: 23 Dec 2006
   Number: 3
-  Version: 80
+  Version: 81
 =head1 Changes to Perl 5 operators
@@ -705,8 +705,18 @@
 to the table above, any existing C<< infix:<~~> >> routines are
 completely ignored.  If the types cannot be matched at compile time,
 one attempt is made to multiply dispatch to all C<< infix:<~~> >>
-infix definitions.  If this fails, the most generic multi definition
-of C<< infix:<~~> >> calls C<===> to match the two variables exactly
+infix definitions.  The standard C<< infix:<~~> >> definitions are
+intended to reproduce as closely as possible the compile-time table above,
+but it can do this based only on the run-time types of the arguments.
+Therefore only the entries above that indicate a type on both sides
+can be dispatched that way.  (You can tell those because both sides
+start with a capital letter.  So multiple dispatch ignores the
+".method", "boolean", "undef", and "*" entries, which are recognized
+syntactically, not by type.)
+If there is no appropriate signature match under the rules of multiple
+dispatch, the most generic multi definition of C<< infix:<~~> >>
+defaults to calling C<===> to match the two variables exactly
 according to their type.  In general you should just rely on this
 and not attempt to define your own C<< infix:<~~> >> operators,
 because complexifying the run-time semantics of C<~~> is not doing
@@ -1264,7 +1274,8 @@
 of metaforms, so we arbitrarily say that no metacircumfix form is
 pregenerated that uses the same grammatical category more than once.
 Therefore forms like C<[+=]> and C<»!===«> and C<X*X=> are generated,
-but not forms like C<»X*X«> or C<X«*»X>.  You do get C<[X*X]>,
+but not forms like C<»X*X«> or C<X«*»X> or C<<< <<+=>>= >>>.
+You do get C<[X*X]>,
 though, because reduction is prefix_circumfix_meta_operator while
 cross operators are infix_circumfix_meta_operator.
@@ -1288,6 +1299,13 @@
 precedence over the C<XxX> operator even if the metaform DFA only
 knows how to recognize the C<XxX> part.
+Note that the maximum possible token length is bounded by the sum
+of the maximum lengths of each metacategory, so an enumerated solution
+is always possible, though perhaps not practical.  It's also the case
+that no metaform is allowed to contain whitespace, so a solution
+that starts at the length of the current "word" and works down is also
 =head1 Junctive operators
 C<|>, C<&>, and C<^> are no longer bitwise operators (see

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