NAME

       Marpa::R2::Semantics::Phases - Phases of SLIF parse evaluation

Overview of the semantic phases

       Most users will not need to read this document.  Most applications will find that the order in which the
       SLIF executes its semantics "just works".  This document describes that order in detail.  These details
       can matter in some applications, for example, those which exploit side effects.  And some readers may
       also find this background material to be helpful.

Parse trees and parse series

       Because Marpa allows ambiguous parsing, each parse can produce a parse series -- a series of zero or more
       parse trees, each with its own parse result.  The first call to the SLIF recognizer's value() method
       after the recognizer is created is the start of the first parse series, and Parse Series Setup Phase
       takes place at this point.

       The first parse series continues until there is a call to the series_restart() method or until the
       recognizer is destroyed.  An application is usually interested in only one parse series.

       The series_restart() method starts a new parse series.  The Parse Series Setup Phase for that parse
       series will take place during the next call of the SLIF recognizer's value() method.

Summary of the phases

       While processing a parse series, we have:

       •   A Parse Series Setup Phase, which occurs during the first call of the SLIF recognizer's value()
           method for that series.  It is followed by

       •   the processing of zero or more parse trees.

       While processing a parse tree, we have:

       •   A Parse Tree Setup Phase, which occurs during the call of the recognizer's value() method for that
           parse tree.  It is followed by

       •   a Parse Tree Traveral Phase.

       Node Evaluation Time is the Tree Traversal Phase, as seen from the point of view of each rule node.  It
       is not a separate phase.

Parse Series Setup Phase

       During the Parse Series Setup Phase all action names are resolved to actions -- Perl scalars or rule
       evaluation closures.  The rule evaluation closures are not called in the Parse Series Setup Phase.  They
       will be called later, in the Parse Tree Traversal Phase.  Also, during the Parse Series Setup Phase, the
       logic which ranks parse trees is executed.

Parse Tree Setup Phase

       In the Parse Tree Setup Phase, the per-parse argument is created.  If a per-parse constructor was found,
       it is run at this point, and the per-parse argument is its return value.  Exactly one Parse Tree Setup
       Phase occurs for each parse tree.

Parse Tree Traversal Phase

       During the Parse Tree Traversal Phase, the rule evaluation closures are called.  Node Evaluation Time is
       the Parse Tree Traversal Phase, as seen from the point of view of the individual nodes of the parse tree.

Copyright and License

         Copyright 2014 Jeffrey Kegler
         This file is part of Marpa::R2.  Marpa::R2 is free software: you can
         redistribute it and/or modify it under the terms of the GNU Lesser
         General Public License as published by the Free Software Foundation,
         either version 3 of the License, or (at your option) any later version.

         Marpa::R2 is distributed in the hope that it will be useful,
         but WITHOUT ANY WARRANTY; without even the implied warranty of
         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
         Lesser General Public License for more details.

         You should have received a copy of the GNU Lesser
         General Public License along with Marpa::R2.  If not, see
         http://www.gnu.org/licenses/.