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Code Issues 15 Releases 21 Activity

Applying simplification to more cases.

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Patrick Lühne 2017-03-23 14:40:21 +01:00
parent 574130a8ec
commit 42e0217409
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GPG Key ID: 05F3611E97A70ABF
1 changed files with 27 additions and 12 deletions
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39
src/anthem/Simplification.cpp
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@ -57,25 +57,42 @@ std::experimental::optional<ast::Term> extractAssignedTerm(ast::Formula &formula
////////////////////////////////////////////////////////////////////////////////////////////////////
// Replaces the first occurrence of a variable with a term in a given formula
// Replaces all occurrences of a variable with a term in a given formula
struct ReplaceVariableWithTermVisitor : public ast::RecursiveFormulaVisitor<ReplaceVariableWithTermVisitor>
{
// Perform replacement in predicates only
static void accept(ast::Predicate &predicate, ast::Formula &, const ast::Variable &variable, ast::Term &&term)
static void accept(ast::Comparison &comparison, ast::Formula &, const ast::Variable &variable, ast::Term &term)
{
if (matchesVariable(comparison.left, variable))
comparison.left = ast::deepCopy(term);
if (matchesVariable(comparison.right, variable))
comparison.right = ast::deepCopy(term);
}
static void accept(ast::In &in, ast::Formula &, const ast::Variable &variable, ast::Term &term)
{
if (matchesVariable(in.element, variable))
in.element = ast::deepCopy(term);
if (matchesVariable(in.set, variable))
in.set = ast::deepCopy(term);
}
static void accept(ast::Predicate &predicate, ast::Formula &, const ast::Variable &variable, ast::Term &term)
{
for (auto &argument : predicate.arguments)
{
if (!matchesVariable(argument, variable))
continue;
argument = std::move(term);
return;
// TODO: optimize (one less deep copy possible)
argument = ast::deepCopy(term);
}
}
// Ignore all other types of expressions
template<class T>
static void accept(T &, ast::Formula &, const ast::Variable &, ast::Term &&)
static void accept(T &, ast::Formula &, const ast::Variable &, ast::Term &)
{
}
};
@ -92,10 +109,6 @@ void simplify(ast::Exists &exists, ast::Formula &formula)
auto &conjunction = exists.argument.get<ast::And>();
auto &arguments = conjunction.arguments;
// Check that formula is in normal form
if (!arguments.back().is<ast::Predicate>() && !arguments.back().is<ast::Not>())
return;
// Simplify formulas of type “exists X (X = t and F(X))” to “F(t)”
for (auto i = exists.variables.begin(); i != exists.variables.end();)
{
@ -106,13 +119,15 @@ void simplify(ast::Exists &exists, ast::Formula &formula)
for (auto j = arguments.begin(); j != arguments.end(); j++)
{
auto &argument = *j;
// Find term that is equivalent to the given variable
auto assignedTerm = extractAssignedTerm(argument, variable);
if (!assignedTerm)
continue;
// If this argument is an assignment of the variable to some other term, remove the assignment and replace the variable with the other term
arguments.back().accept(ReplaceVariableWithTermVisitor(), arguments.back(), variable, std::move(assignedTerm.value()));
// Replace all occurrences of the variable with the equivalent term
for (auto &otherArgument : arguments)
otherArgument.accept(ReplaceVariableWithTermVisitor(), otherArgument, variable, assignedTerm.value());
arguments.erase(j);
wasVariableReplaced = true;