NAME

       Makefile::AST::Evaluator - Evaluator and runtime for Makefile::AST instances

SYNOPSIS

           use Makefile::AST::Evaluator;

           $Makefile::AST::Evaluator::JustPrint = 0;
           $Makefile::AST::Evaluator::Quiet = 1;
           $Makefile::AST::Evaluator::IgnoreErrors = 1;
           $Makefile::AST::Evaluator::AlwaysMake = 1;
           $Makefile::AST::Evaluator::Question = 1;

           # $ast is a Makefile::AST instance:
           my $eval = Makefile::AST::Evaluator->new($ast);

           Makefile::AST::Evaluator->add_trigger(
               firing_rule => sub {
                   my ($self, $rule, $ast_cmds) = @_;
                   my $target = $rule->target;
                   my $colon = $rule->colon;
                   my @normal_prereqs = @{ $rule->normal_prereqs };
                   # ...
               }
           );
           $eval->set_required_target($user_makefile)
           $eval->make($goal);

DESCRIPTION

       This module implementes an evaluator or a runtime for makefile ASTs represented by
       Makefile::AST instances.

       It "executes" the specified GNU make AST by the GNU makefile semantics. Note that,
       "execution" not necessarily mean building a project tree by firing makefile rule commands.
       Actually you can defining your own triggers by calling the add_trigger method. (See the
       "SYNOPSIS" for examples.) In other words, you can do more interesting things like plotting
       the call path tree of a Makefile using Graphviz, or translating the original makefile to
       another form (like what the makesimple script does).

       It's worth mentioning that, most of the construction algorithm for topological graph s
       (including implicit rule application) have already been implemented in Makefile::AST and
       its child node classes.

CONFIGURE VARIABLES

       This module provides several package variables (i.e. static class variables) for
       controlling the behavior of the evaluator.

       Particularly the user needs to set the $AlwaysMake variable to true and $Question to true,
       if she wants to use the evaluator to do special tasks like plotting dependency graphs and
       translating GNU makefiles to other format.

       Setting $AlwaysMake to true will force the evaluator to ignore the timestamps of external
       files appeared in the makefiles while setting $Question to true will prevent the evaluator
       from executing the shell commands specified in the makefile rules.

       Here's the detailed listing for all the config variables:

       $Question
           This variable corresponds to the command-line option "-q" or <--question> in GNU make.
           Its purpose is to make the evaluator enter the "questioning mode", i.e., a mode in
           which "make" will never try executing rule commands unless it has to, "and" echoing is
           suppressed at the same time.

       $AlwaysMake
           This variable corresponds to the command-line option "-B" or "--always-make". It
           forces re-constructing all the rule's targets related to the goal, ignoring the
           timestamp or existence of targets' dependencies.

       $Quiet
           It corresponds to GNU make's command-line option "-s", "--silent", or "--quiet". Its
           effect is to cancel the echoing of shell commands being executed.

       $JustPrint
           This variable corresponds to GNU make's command line option "-n", "--just-print",
           "--dry-run", or "--recon". Its effect is to print out the shell commands requiring
           execution but without actually executing them.

       $IgnoreErrors
           This variable corresponds to GNU make's command line option "-i" or
           "--ignore-errors"XIt's used to ignore the errors of shell commands being executed
           during the make process. The default behavior is quitting as soon as a shell command
           without the "-" modifier fails.

CLASS TRIGGERS

       The "make_by_rule" method of this class defines a trigger named "firing_rule" via the
       Class::Trait module. Everytime the "make_by_rule" method reaches the trigger point, it
       will invoke the user's processing handler with the following three arguments: the self
       object, the Makefile::AST::Rule object, and the corresponding "Makefile::AST::Command"
       object in the context.

       By registering his own processing handlers for the "firing_rule" trigger, the user's code
       can reuse the evaluator to do his own cool things without traversing the makefile ASTs
       himself.

       See the "SYNOPSIS" for code examples.

CODE REPOSITORY

       For the very latest version of this script, check out the source from

       http://github.com/agentzh/makefile-parser-pm <http://github.com/agentzh/makefile-parser-
       pm>.

       There is anonymous access to all.

AUTHOR

       Zhang "agentzh" Yichun "<agentzh@gmail.com>"

COPYRIGHT AND LICENSE

       Copyright (c) 2007-2008 by Zhang "agentzh" Yichun (agentzh).

       This library is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

SEE ALSO

       Makefile::AST, Makefile::Parser::GmakeDB, pgmake-db, makesimple, Makefile::DOM.