Example 6 with NormalHead
use of at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead in project Alpha by alpha-asp.
the class EnumerationRewriting method rewriteRules.
private List<Rule<Head>> rewriteRules(List<Rule<Head>> srcRules, Predicate enumPredicate) {
List<Rule<Head>> rewrittenRules = new ArrayList<>();
for (Rule<Head> rule : srcRules) {
if (rule.getHead() != null && !(rule.getHead() instanceof NormalHead)) {
throw oops("Encountered rule whose head is not normal: " + rule);
}
if (rule.getHead() != null && ((NormalHead) rule.getHead()).getAtom().getPredicate().equals(enumPredicate)) {
throw oops("Atom declared as enumeration atom by directive occurs in head of the rule: " + rule);
}
List<Literal> modifiedBodyLiterals = new ArrayList<>(rule.getBody());
Iterator<Literal> rit = modifiedBodyLiterals.iterator();
LinkedList<Literal> rewrittenLiterals = new LinkedList<>();
while (rit.hasNext()) {
Literal literal = rit.next();
if (!(literal instanceof BasicLiteral)) {
continue;
}
BasicLiteral basicLiteral = (BasicLiteral) literal;
if (!basicLiteral.getPredicate().equals(enumPredicate)) {
continue;
}
// basicLiteral is an enumeration literal (i.e. predicate is marked as enum using directive)
rit.remove();
Term enumIdTerm = basicLiteral.getAtom().getTerms().get(0);
Term valueTerm = basicLiteral.getAtom().getTerms().get(1);
VariableTerm indexTerm = (VariableTerm) basicLiteral.getAtom().getTerms().get(2);
rewrittenLiterals.add(new EnumerationAtom(enumIdTerm, valueTerm, indexTerm).toLiteral());
}
modifiedBodyLiterals.addAll(rewrittenLiterals);
rewrittenRules.add(new BasicRule(rule.getHead(), modifiedBodyLiterals));
}
return rewrittenRules;
}
Also used :
BasicRule(at.ac.tuwien.kr.alpha.core.rules.BasicRule)
Head(at.ac.tuwien.kr.alpha.api.rules.heads.Head)
NormalHead(at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead)
ArrayList(java.util.ArrayList)
Term(at.ac.tuwien.kr.alpha.api.terms.Term)
VariableTerm(at.ac.tuwien.kr.alpha.api.terms.VariableTerm)
LinkedList(java.util.LinkedList)
BasicLiteral(at.ac.tuwien.kr.alpha.api.programs.literals.BasicLiteral)
NormalHead(at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead)
Literal(at.ac.tuwien.kr.alpha.api.programs.literals.Literal)
BasicLiteral(at.ac.tuwien.kr.alpha.api.programs.literals.BasicLiteral)
EnumerationAtom(at.ac.tuwien.kr.alpha.core.atoms.EnumerationAtom)
VariableTerm(at.ac.tuwien.kr.alpha.api.terms.VariableTerm)
Rule(at.ac.tuwien.kr.alpha.api.rules.Rule)
BasicRule(at.ac.tuwien.kr.alpha.core.rules.BasicRule)
Example 7 with NormalHead
use of at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead in project Alpha by alpha-asp.
the class VariableEqualityRemoval method findAndReplaceVariableEquality.
private Rule<Head> findAndReplaceVariableEquality(Rule<Head> rule) {
// Collect all equal variables.
HashMap<VariableTerm, HashSet<VariableTerm>> variableToEqualVariables = new LinkedHashMap<>();
HashSet<Literal> equalitiesToRemove = new HashSet<>();
for (Literal bodyElement : rule.getBody()) {
if (!(bodyElement instanceof ComparisonLiteral)) {
continue;
}
ComparisonLiteral comparisonLiteral = (ComparisonLiteral) bodyElement;
if (!comparisonLiteral.isNormalizedEquality()) {
continue;
}
if (comparisonLiteral.getTerms().get(0) instanceof VariableTerm && comparisonLiteral.getTerms().get(1) instanceof VariableTerm) {
VariableTerm leftVariable = (VariableTerm) comparisonLiteral.getTerms().get(0);
VariableTerm rightVariable = (VariableTerm) comparisonLiteral.getTerms().get(1);
HashSet<VariableTerm> leftEqualVariables = variableToEqualVariables.get(leftVariable);
HashSet<VariableTerm> rightEqualVariables = variableToEqualVariables.get(rightVariable);
if (leftEqualVariables == null && rightEqualVariables == null) {
HashSet<VariableTerm> equalVariables = new LinkedHashSet<>(Arrays.asList(leftVariable, rightVariable));
variableToEqualVariables.put(leftVariable, equalVariables);
variableToEqualVariables.put(rightVariable, equalVariables);
}
if (leftEqualVariables == null && rightEqualVariables != null) {
rightEqualVariables.add(leftVariable);
variableToEqualVariables.put(leftVariable, rightEqualVariables);
}
if (leftEqualVariables != null && rightEqualVariables == null) {
leftEqualVariables.add(rightVariable);
variableToEqualVariables.put(rightVariable, leftEqualVariables);
}
if (leftEqualVariables != null && rightEqualVariables != null) {
leftEqualVariables.addAll(rightEqualVariables);
for (VariableTerm rightEqualVariable : rightEqualVariables) {
variableToEqualVariables.put(rightEqualVariable, leftEqualVariables);
}
}
equalitiesToRemove.add(comparisonLiteral);
}
}
if (variableToEqualVariables.isEmpty()) {
// Skip rule if there is no equality between variables.
return rule;
}
List<Literal> rewrittenBody = new ArrayList<>(rule.getBody());
if (!rule.isConstraint() && rule.getHead() instanceof DisjunctiveHead) {
throw new UnsupportedOperationException("VariableEqualityRemoval cannot be applied to rule with DisjunctiveHead, yet.");
}
NormalHead rewrittenHead = rule.isConstraint() ? null : Heads.newNormalHead(((NormalHead) rule.getHead()).getAtom());
// Use substitution for actual replacement.
Unifier replacementSubstitution = new Unifier();
// For each set of equal variables, take the first variable and replace all others by it.
for (Map.Entry<VariableTerm, HashSet<VariableTerm>> variableEqualityEntry : variableToEqualVariables.entrySet()) {
VariableTerm variableToReplace = variableEqualityEntry.getKey();
VariableTerm replacementVariable = variableEqualityEntry.getValue().iterator().next();
if (variableToReplace == replacementVariable) {
continue;
}
replacementSubstitution.put(variableToReplace, replacementVariable);
}
// Replace/Substitute in each literal every term where one of the common variables occurs.
Iterator<Literal> bodyIterator = rewrittenBody.iterator();
while (bodyIterator.hasNext()) {
Literal literal = bodyIterator.next();
if (equalitiesToRemove.contains(literal)) {
bodyIterator.remove();
}
for (int i = 0; i < literal.getTerms().size(); i++) {
Term replaced = literal.getTerms().get(i).substitute(replacementSubstitution);
literal.getTerms().set(i, replaced);
}
}
// Replace variables in head.
if (rewrittenHead != null) {
Atom headAtom = rewrittenHead.getAtom();
for (int i = 0; i < headAtom.getTerms().size(); i++) {
Term replaced = headAtom.getTerms().get(i).substitute(replacementSubstitution);
headAtom.getTerms().set(i, replaced);
}
}
return new BasicRule(rewrittenHead, rewrittenBody);
}
Also used :
LinkedHashSet(java.util.LinkedHashSet)
BasicRule(at.ac.tuwien.kr.alpha.core.rules.BasicRule)
ArrayList(java.util.ArrayList)
DisjunctiveHead(at.ac.tuwien.kr.alpha.api.rules.heads.DisjunctiveHead)
Term(at.ac.tuwien.kr.alpha.api.terms.Term)
VariableTerm(at.ac.tuwien.kr.alpha.api.terms.VariableTerm)
Atom(at.ac.tuwien.kr.alpha.api.programs.atoms.Atom)
LinkedHashMap(java.util.LinkedHashMap)
NormalHead(at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead)
Literal(at.ac.tuwien.kr.alpha.api.programs.literals.Literal)
ComparisonLiteral(at.ac.tuwien.kr.alpha.api.programs.literals.ComparisonLiteral)
VariableTerm(at.ac.tuwien.kr.alpha.api.terms.VariableTerm)
ComparisonLiteral(at.ac.tuwien.kr.alpha.api.programs.literals.ComparisonLiteral)
HashMap(java.util.HashMap)
LinkedHashMap(java.util.LinkedHashMap)
Map(java.util.Map)
Unifier(at.ac.tuwien.kr.alpha.commons.substitutions.Unifier)
HashSet(java.util.HashSet)
LinkedHashSet(java.util.LinkedHashSet)
Aggregations
Literal (at.ac.tuwien.kr.alpha.api.programs.literals.Literal)7
NormalHead (at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead)7
ArrayList (java.util.ArrayList)6
VariableTerm (at.ac.tuwien.kr.alpha.api.terms.VariableTerm)5
BasicRule (at.ac.tuwien.kr.alpha.core.rules.BasicRule)4
ComparisonLiteral (at.ac.tuwien.kr.alpha.api.programs.literals.ComparisonLiteral)3
AggregateAtom (at.ac.tuwien.kr.alpha.api.programs.atoms.AggregateAtom)2
BasicAtom (at.ac.tuwien.kr.alpha.api.programs.atoms.BasicAtom)2
BasicLiteral (at.ac.tuwien.kr.alpha.api.programs.literals.BasicLiteral)2
Head (at.ac.tuwien.kr.alpha.api.rules.heads.Head)2
Term (at.ac.tuwien.kr.alpha.api.terms.Term)2
NormalRuleImpl (at.ac.tuwien.kr.alpha.core.rules.NormalRuleImpl)2
HashSet (java.util.HashSet)2
LinkedHashMap (java.util.LinkedHashMap)2
Map (java.util.Map)2
ComparisonOperator (at.ac.tuwien.kr.alpha.api.ComparisonOperator)1
Atom (at.ac.tuwien.kr.alpha.api.programs.atoms.Atom)1
AggregateLiteral (at.ac.tuwien.kr.alpha.api.programs.literals.AggregateLiteral)1
Rule (at.ac.tuwien.kr.alpha.api.rules.Rule)1
DisjunctiveHead (at.ac.tuwien.kr.alpha.api.rules.heads.DisjunctiveHead)1
