Author: larry Date: Mon May 8 17:26:05 2006 New Revision: 9139 Modified: doc/trunk/design/syn/S02.pod
Log: Clarification of the 0,1,Inf parsing policy. Modified: doc/trunk/design/syn/S02.pod ============================================================================== --- doc/trunk/design/syn/S02.pod (original) +++ doc/trunk/design/syn/S02.pod Mon May 8 17:26:05 2006 @@ -12,9 +12,9 @@ Maintainer: Larry Wall <[EMAIL PROTECTED]> Date: 10 Aug 2004 - Last Modified: 6 May 2006 + Last Modified: 8 May 2006 Number: 2 - Version: 38 + Version: 39 This document summarizes Apocalypse 2, which covers small-scale lexical items and typological issues. (These Synopses also contain @@ -1615,9 +1615,9 @@ visible at the point of the controlling C<proto> declaration. Parsing of a bareword function as a provisional call is always done -the same way list operators are treated. If a postdeclaration bends -the syntax to be inconsistent with that, it is an error of the -inconsistent signature variety. +the same way list operators are treated. If a postdeclaration +bends the syntax to be inconsistent with that, it is an error of +the inconsistent signature variety. If the unrecognized subroutine name is followed by C<< postcircumfix:<( )> >>, it is compiled as a provisional function call of the parenthesized form. @@ -1628,6 +1628,31 @@ arguments, whereas anything following whitespace will be interpreted as an argument list if possible. +Based on the signature of the subroutine declaration, there are only +four ways that an argument list can be parsed: + + Signature # of expected args + () 0 + ($x) 1 + ($x?) 0..1 + (anything else) 0..Inf + +That is, a standard subroutine call may be parsed only as a 0-arg term +(or function call), a 1-mandatory-arg prefix operator (or function +call), a 1-optional-arg term or prefix operator (or function call), or +an "infinite-arg" list operator (or function call). A given signature +might only accept 2 arguments, but the only number distinctions the +parser is allowed to make is between void, singular and plural; +checking that number of arguments supplied matches some number +larger than one must be done as a separate semantic constraint, not +as a syntactic constraint. Perl functions never take N arguments +off of a list and leave the rest for someone else, except for small +values of N, where small is defined as not more than 1. You can get +fancier using macros, but macros I<always> require predeclaration. +Since the non-infinite-list forms are essentially behaving as macros, +those forms also require predeclaration. Only the infinite-list form +may be postdeclared (and hence used provisionally). + It is illegal for a provisional subroutine call to be followed by a colon postfix, since such a colon is allowed only on an indirect object, or a method call in dot form. (It is also allowed on a label when a
