Refactored formula simplification with Clingo’s variants.
This commit is contained in:
@@ -1,7 +1,5 @@
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#include <anthem/Simplification.h>
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#include <iostream>
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namespace anthem
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{
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@@ -13,92 +11,139 @@ namespace anthem
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bool isPrimitiveTerm(const ast::Term &term)
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{
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const auto handleBinaryOperation =
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[](const ast::BinaryOperationPointer &)
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{
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return false;
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};
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const auto handleInterval =
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[](const ast::IntervalPointer &)
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{
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return false;
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};
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const auto handleDefault =
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[](const auto &)
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{
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return true;
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};
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return term.match(handleBinaryOperation, handleInterval, handleDefault);
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return (!term.is<ast::BinaryOperation>() && !term.is<ast::Interval>());
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}
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////////////////////////////////////////////////////////////////////////////////////////////////////
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bool matchesVariable(const ast::Term &term, const ast::VariablePointer &variable)
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template<class T>
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struct RecursiveFormulaVisitor
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{
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const auto handleVariable =
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[&](const ast::VariablePointer &other)
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{
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return variable->name == other->name;
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};
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void visit(ast::And &and_, ast::Formula &formula)
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{
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for (auto &argument : and_.arguments)
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argument.accept(*this, argument);
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const auto handleDefault =
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[](const auto &)
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{
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return false;
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};
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return T::accept(and_, formula);
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}
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return term.match(handleVariable, handleDefault);
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void visit(ast::Biconditional &biconditional, ast::Formula &formula)
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{
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biconditional.left.accept(*this, biconditional.left);
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biconditional.right.accept(*this, biconditional.right);
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return T::accept(biconditional, formula);
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}
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void visit(ast::Boolean &boolean, ast::Formula &formula)
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{
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return T::accept(boolean, formula);
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}
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void visit(ast::Comparison &comparison, ast::Formula &formula)
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{
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return T::accept(comparison, formula);
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}
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void visit(ast::Exists &exists, ast::Formula &formula)
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{
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exists.argument.accept(*this, exists.argument);
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return T::accept(exists, formula);
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}
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void visit(ast::ForAll &forAll, ast::Formula &formula)
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{
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forAll.argument.accept(*this, forAll.argument);
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return T::accept(forAll, formula);
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}
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void visit(ast::Implies &implies, ast::Formula &formula)
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{
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implies.antecedent.accept(*this, implies.antecedent);
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implies.consequent.accept(*this, implies.consequent);
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return T::accept(implies, formula);
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}
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void visit(ast::In &in, ast::Formula &formula)
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{
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return T::accept(in, formula);
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}
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void visit(ast::Not ¬_, ast::Formula &formula)
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{
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not_.argument.accept(*this, not_.argument);
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return T::accept(not_, formula);
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}
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void visit(ast::Or &or_, ast::Formula &formula)
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{
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for (auto &argument : or_.arguments)
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argument.accept(*this, argument);
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return T::accept(or_, formula);
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}
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void visit(ast::Predicate &predicate, ast::Formula &formula)
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{
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return T::accept(predicate, formula);
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}
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};
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////////////////////////////////////////////////////////////////////////////////////////////////////
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bool matchesVariable(const ast::Term &term, const ast::Variable &variable)
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{
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if (!term.is<ast::Variable>())
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return false;
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const auto otherVariable = term.get<ast::Variable>();
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return variable.name == otherVariable.name;
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}
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////////////////////////////////////////////////////////////////////////////////////////////////////
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std::experimental::optional<ast::Term> extractAssignedTerm(ast::Formula &formula, const ast::VariablePointer &variable)
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std::experimental::optional<ast::Term> extractAssignedTerm(ast::Formula &formula, const ast::Variable &variable)
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{
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const auto handleComparison =
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[&](ast::ComparisonPointer &comparison) -> std::experimental::optional<ast::Term>
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{
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if (comparison->operator_ != ast::Comparison::Operator::Equal)
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return std::experimental::nullopt;
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if (!formula.is<ast::Comparison>())
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return std::experimental::nullopt;
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if (matchesVariable(comparison->left, variable))
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return std::move(comparison->right);
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auto &comparison = formula.get<ast::Comparison>();
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if (matchesVariable(comparison->right, variable))
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return std::move(comparison->left);
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if (comparison.operator_ != ast::Comparison::Operator::Equal)
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return std::experimental::nullopt;
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return std::experimental::nullopt;
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};
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if (matchesVariable(comparison.left, variable))
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return std::move(comparison.right);
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const auto handleDefault =
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[](auto &) -> std::experimental::optional<ast::Term>
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{
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return std::experimental::nullopt;
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};
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if (matchesVariable(comparison.right, variable))
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return std::move(comparison.left);
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return formula.match(handleComparison, handleDefault);
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return std::experimental::nullopt;
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}
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////////////////////////////////////////////////////////////////////////////////////////////////////
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ast::Formula simplify(ast::ExistsPointer &exists)
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void simplify(ast::Exists &exists, ast::Formula &formula)
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{
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if (!exists->argument.is<ast::AndPointer>())
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return std::move(exists);
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if (!exists.argument.is<ast::And>())
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return;
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auto &conjunction = exists->argument.get_unchecked<ast::AndPointer>();
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auto &arguments = conjunction->arguments;
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auto &conjunction = exists.argument.get<ast::And>();
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auto &arguments = conjunction.arguments;
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// Check that formula is in normal form
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if (!arguments.back().is<ast::PredicatePointer>())
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return std::move(exists);
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if (!arguments.back().is<ast::Predicate>())
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return;
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const auto replaceVariableInPredicateWithTerm =
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[](ast::PredicatePointer &predicate, const ast::VariablePointer &variable, ast::Term &&term)
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[](ast::Predicate &predicate, const ast::Variable &variable, ast::Term &term)
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{
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for (auto &argument : predicate->arguments)
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for (auto &argument : predicate.arguments)
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{
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if (!matchesVariable(argument, variable))
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continue;
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@@ -109,7 +154,7 @@ ast::Formula simplify(ast::ExistsPointer &exists)
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};
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// Simplify formulas of type “exists X (X = t and F(Y))” to “F(t)”
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for (auto i = exists->variables.begin(); i != exists->variables.end();)
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for (auto i = exists.variables.begin(); i != exists.variables.end();)
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{
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auto &variable = *i;
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@@ -123,10 +168,10 @@ ast::Formula simplify(ast::ExistsPointer &exists)
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if (!assignedTerm)
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continue;
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auto &lastArgument = arguments.back().get_unchecked<ast::PredicatePointer>();
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auto &lastArgument = arguments.back().get<ast::Predicate>();
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// If this argument is an assignment of the variable to some other term, remove the assignment and replace the variable with the other term
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replaceVariableInPredicateWithTerm(lastArgument, variable, std::move(assignedTerm.value()));
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replaceVariableInPredicateWithTerm(lastArgument, variable, assignedTerm.value());
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arguments.erase(j);
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wasVariableReplaced = true;
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@@ -135,107 +180,60 @@ ast::Formula simplify(ast::ExistsPointer &exists)
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if (wasVariableReplaced)
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{
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i = exists->variables.erase(i);
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i = exists.variables.erase(i);
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continue;
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}
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i++;
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}
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if (exists->variables.empty())
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// If there are still variables, do nothing more
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if (!exists.variables.empty())
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return;
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assert(!conjunction.arguments.empty());
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// If the argument is a conjunction with just one element, directly replace the input formula with the argument
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if (conjunction.arguments.size() == 1)
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{
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assert(!conjunction->arguments.empty());
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if (conjunction->arguments.size() == 1)
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return std::move(conjunction->arguments.front());
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return std::move(exists->argument);
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auto test = std::move(conjunction.arguments.front());
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formula = std::move(test);
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return;
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}
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return std::move(exists);
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// If there is more than one element in the conjunction, replace the input formula with the conjunction
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formula = std::move(exists.argument);
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}
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////////////////////////////////////////////////////////////////////////////////////////////////////
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ast::Formula simplify(ast::Formula &&formula)
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struct SimplifyFormulaVisitor : public RecursiveFormulaVisitor<SimplifyFormulaVisitor>
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{
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const auto handleAnd =
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[&](ast::AndPointer &and_) -> ast::Formula
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{
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for (auto &argument : and_->arguments)
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argument = simplify(std::move(argument));
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static void accept(ast::Exists &exists, ast::Formula &formula)
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{
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simplify(exists, formula);
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}
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return std::move(and_);
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};
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static void accept(ast::In &in, ast::Formula &formula)
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{
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if (!isPrimitiveTerm(in.element) || !isPrimitiveTerm(in.set))
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return;
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const auto handleBiconditional =
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[&](ast::BiconditionalPointer &biconditional) -> ast::Formula
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{
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biconditional->left = simplify(std::move(biconditional->left));
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biconditional->right = simplify(std::move(biconditional->right));
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// Simplify formulas of type “A in B” to “A = B” if A and B are primitive
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formula = ast::Comparison(ast::Comparison::Operator::Equal, std::move(in.element), std::move(in.set));
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}
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return std::move(biconditional);
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};
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template<class T>
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static void accept(T &, ast::Formula &)
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{
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}
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};
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const auto handleExists =
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[&](ast::ExistsPointer &exists) -> ast::Formula
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{
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exists->argument = simplify(std::move(exists->argument));
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////////////////////////////////////////////////////////////////////////////////////////////////////
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return simplify(exists);
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};
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const auto handleForAll =
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[&](ast::ForAllPointer &forAll) -> ast::Formula
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{
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forAll->argument = simplify(std::move(forAll->argument));
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return std::move(forAll);
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};
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const auto handleImplies =
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[&](ast::ImpliesPointer &implies) -> ast::Formula
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{
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implies->antecedent = simplify(std::move(implies->antecedent));
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implies->consequent = simplify(std::move(implies->consequent));
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return std::move(implies);
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};
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const auto handleIn =
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[](ast::InPointer &in) -> ast::Formula
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{
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if (!isPrimitiveTerm(in->element) || !isPrimitiveTerm(in->set))
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return std::move(in);
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// Simplify formulas of type “A in B” to “A = B” if A and B are primitive
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return std::make_unique<ast::Comparison>(ast::Comparison::Operator::Equal, std::move(in->element), std::move(in->set));
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};
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const auto handleNot =
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[&](ast::NotPointer ¬_) -> ast::Formula
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{
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not_->argument = simplify(std::move(not_->argument));
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return std::move(not_);
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};
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const auto handleOr =
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[&](ast::OrPointer &or_) -> ast::Formula
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{
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for (auto &argument : or_->arguments)
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argument = simplify(std::move(argument));
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return std::move(or_);
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};
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const auto handleDefault =
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[&](auto &x) -> ast::Formula
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{
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return std::move(x);
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};
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return formula.match(handleAnd, handleBiconditional, handleExists, handleForAll, handleImplies, handleIn, handleNot, handleOr, handleDefault);
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void simplify(ast::Formula &formula)
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{
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formula.accept(SimplifyFormulaVisitor(), formula);
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}
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////////////////////////////////////////////////////////////////////////////////////////////////////
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@@ -53,8 +53,8 @@ void translate(const char *fileName, std::istream &stream, Context &context)
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return;
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}
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auto simplifiedFormula = simplify(std::move(formula.value()));
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context.logger.outputStream() << simplifiedFormula << std::endl;
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simplify(formula.value());
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context.logger.outputStream() << formula.value() << std::endl;
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};
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const auto logger =
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