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  0   €l–дY>” TК:”эЖ™ё'”ЕЈБ„auя_‹uРb&=LV[(БА ;K    # Copyright (C) 1997-2020 Free Software Foundation, Inc.

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.

# This program 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 General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

package Automake::Condition;

use 5.006;
use strict;
use Carp;

require Exporter;
use vars '@ISA', '@EXPORT_OK';
@ISA = qw/Exporter/;
@EXPORT_OK = qw/TRUE FALSE reduce_and reduce_or/;

=head1 NAME

Automake::Condition - record a conjunction of conditionals

=head1 SYNOPSIS

  use Automake::Condition;

  # Create a condition to represent "COND1 and not COND2".
  my $cond = new Automake::Condition "COND1_TRUE", "COND2_FALSE";
  # Create a condition to represent "not COND3".
  my $other = new Automake::Condition "COND3_FALSE";

  # Create a condition to represent
  #   "COND1 and not COND2 and not COND3".
  my $both = $cond->merge ($other);

  # Likewise, but using a list of conditional strings
  my $both2 = $cond->merge_conds ("COND3_FALSE");

  # Strip from $both any subconditions which are in $other.
  # This is the opposite of merge.
  $cond = $both->strip ($other);

  # Return the list of conditions ("COND1_TRUE", "COND2_FALSE"):
  my @conds = $cond->conds;

  # Is $cond always true?  (Not in this example)
  if ($cond->true) { ... }

  # Is $cond always false? (Not in this example)
  if ($cond->false) { ... }

  # Return the list of conditionals as a string:
  #  "COND1_TRUE COND2_FALSE"
  my $str = $cond->string;

  # Return the list of conditionals as a human readable string:
  #  "COND1 and !COND2"
  my $str = $cond->human;

  # Return the list of conditionals as a AC_SUBST-style string:
  #  "@COND1_TRUE@@COND2_FALSE@"
  my $subst = $cond->subst_string;

  # Is $cond true when $both is true?  (Yes in this example)
  if ($cond->true_when ($both)) { ... }

  # Is $cond redundant w.r.t. {$other, $both}?
  # (Yes in this example)
  if ($cond->redundant_wrt ($other, $both)) { ... }

  # Does $cond imply any of {$other, $both}?
  # (Not in this example)
  if ($cond->implies_any ($other, $both)) { ... }

  # Remove superfluous conditionals assuming they will eventually
  # be multiplied together.
  # (Returns @conds = ($both) in this example, because
  # $other and $cond are implied by $both.)
  @conds = Automake::Condition::reduce_and ($other, $both, $cond);

  # Remove superfluous conditionals assuming they will eventually
  # be summed together.
  # (Returns @conds = ($cond, $other) in this example, because
  # $both is a subset condition of $cond: $cond is true whenever $both
  # is true.)
  @conds = Automake::Condition::reduce_or ($other, $both, $cond);

  # Invert a Condition.  This returns a list of Conditions.
  @conds = $both->not;

=head1 DESCRIPTION

A C<Condition> is a conjunction of conditionals (i.e., atomic conditions
defined in F<configure.ac> by C<AM_CONDITIONAL>.  In Automake they
are used to represent the conditions into which F<Makefile> variables and
F<Makefile> rules are defined.

If the variable C<VAR> is defined as

  if COND1
    if COND2
      VAR = value
    endif
  endif

then it will be associated a C<Condition> created with
the following statement.

  new Automake::Condition "COND1_TRUE", "COND2_TRUE";

Remember that a C<Condition> is a I<conjunction> of conditionals, so
the above C<Condition> means C<VAR> is defined when C<COND1>
B<and> C<COND2> are true. There is no way to express disjunctions
(i.e., I<or>s) with this class (but see L<DisjConditions>).

Another point worth to mention is that each C<Condition> object is
unique with respect to its condition