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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchlib.rankingexpression.rule;
import com.yahoo.searchlib.rankingexpression.Reference;
import com.yahoo.searchlib.rankingexpression.evaluation.Context;
import com.yahoo.searchlib.rankingexpression.evaluation.MapContext;
import com.yahoo.searchlib.rankingexpression.evaluation.Value;
import com.yahoo.tensor.TensorType;
import com.yahoo.tensor.evaluation.TypeContext;
import java.util.Collections;
import java.util.Deque;
import java.util.HashSet;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.function.DoubleBinaryOperator;
import java.util.function.DoubleUnaryOperator;
import java.util.stream.Collectors;
/**
* A free, parametrized function
*
* @author bratseth
*/
public class LambdaFunctionNode extends CompositeNode {
private final List<String> arguments;
private final ExpressionNode functionExpression;
public LambdaFunctionNode(List<String> arguments, ExpressionNode functionExpression) {
if ( ! arguments.containsAll(featuresAccessedIn(functionExpression))) {
throw new IllegalArgumentException("Lambda " + functionExpression + " accesses features outside its scope: " +
featuresAccessedIn(functionExpression).stream()
.filter(f -> ! arguments.contains(f))
.collect(Collectors.joining(", ")));
}
this.arguments = List.copyOf(arguments);
this.functionExpression = functionExpression;
}
@Override
public List<ExpressionNode> children() {
return Collections.singletonList(functionExpression);
}
@Override
public CompositeNode setChildren(List<ExpressionNode> children) {
if ( children.size() != 1)
throw new IllegalArgumentException("A lambda function must have a single child expression");
return new LambdaFunctionNode(arguments, children.get(0));
}
@Override
public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
string.append("f(").append(commaSeparated(arguments)).append(")(");
return functionExpression.toString(string, context, path, this).append(")");
}
private String commaSeparated(List<String> list) {
StringBuilder b = new StringBuilder();
for (String element : list)
b.append(element).append(",");
if (b.length() > 0)
b.setLength(b.length()-1);
return b.toString();
}
@Override
public TensorType type(TypeContext<Reference> context) {
return TensorType.empty; // by definition - no nested lambdas
}
/** Evaluate this in a context which must have the arguments bound */
@Override
public Value evaluate(Context context) {
return functionExpression.evaluate(context);
}
/**
* Returns this as a double unary operator
*
* @throws IllegalStateException if this has more than one argument
*/
public DoubleUnaryOperator asDoubleUnaryOperator() {
if (arguments.size() > 1)
throw new IllegalStateException("Cannot apply " + this + " as a DoubleUnaryOperator: " +
"Must have at most one argument " + " but has " + arguments);
return new DoubleUnaryLambda();
}
/**
* Returns this as a double binary operator
*
* @throws IllegalStateException if this has more than two arguments
*/
public DoubleBinaryOperator asDoubleBinaryOperator() {
if (arguments.size() > 2)
throw new IllegalStateException("Cannot apply " + this + " as a DoubleBinaryOperator: " +
"Must have at most two argument " + " but has " + arguments);
// Optimization: if possible, calculate directly rather than creating a context and evaluating the expression
return getDirectEvaluator().orElseGet(DoubleBinaryLambda::new);
}
private Optional<DoubleBinaryOperator> getDirectEvaluator() {
if ( ! (functionExpression instanceof OperationNode node)) {
return Optional.empty();
}
if ( ! (node.children().get(0) instanceof ReferenceNode lhs) || ! (node.children().get(1) instanceof ReferenceNode rhs)) {
return Optional.empty();
}
if (! lhs.getName().equals(arguments.get(0)) || ! rhs.getName().equals(arguments.get(1))) {
return Optional.empty();
}
if (node.operators().size() != 1) {
return Optional.empty();
}
Operator operator = node.operators().get(0);
return switch (operator) {
case or -> asFunctionExpression((left, right) -> ((left != 0.0) || (right != 0.0)) ? 1.0 : 0.0);
case and -> asFunctionExpression((left, right) -> ((left != 0.0) && (right != 0.0)) ? 1.0 : 0.0);
case plus -> asFunctionExpression((left, right) -> left + right);
case minus -> asFunctionExpression((left, right) -> left - right);
case multiply -> asFunctionExpression((left, right) -> left * right);
case divide -> asFunctionExpression((left, right) -> left / right);
case modulo -> asFunctionExpression((left, right) -> left % right);
case power -> asFunctionExpression(Math::pow);
default -> Optional.empty();
};
}
private Optional<DoubleBinaryOperator> asFunctionExpression(DoubleBinaryOperator operator) {
return Optional.of(new DoubleBinaryOperator() {
@Override
public double applyAsDouble(double left, double right) {
return operator.applyAsDouble(left, right);
}
@Override
public String toString() {
return LambdaFunctionNode.this.toString();
}
});
}
private static Set<String> featuresAccessedIn(ExpressionNode node) {
if (node instanceof ReferenceNode) {
return Set.of(((ReferenceNode) node).reference().toString());
}
else if (node instanceof NameNode) { // (This clause probably not necessary)
return Set.of(((NameNode) node).getValue());
}
else if (node instanceof CompositeNode) {
Set<String> features = new HashSet<>();
((CompositeNode)node).children().forEach(child -> features.addAll(featuresAccessedIn(child)));
return features;
}
return Set.of();
}
@Override
public int hashCode() { return Objects.hash("lambdaFunction", arguments, functionExpression); }
private class DoubleUnaryLambda implements DoubleUnaryOperator {
@Override
public double applyAsDouble(double operand) {
MapContext context = new MapContext();
if (arguments.size() > 0)
context.put(arguments.get(0), operand);
return evaluate(context).asDouble();
}
@Override
public String toString() {
return LambdaFunctionNode.this.toString();
}
}
private class DoubleBinaryLambda implements DoubleBinaryOperator {
@Override
public double applyAsDouble(double left, double right) {
MapContext context = new MapContext();
if (arguments.size() > 0)
context.put(arguments.get(0), left);
if (arguments.size() > 1)
context.put(arguments.get(1), right);
return evaluate(context).asDouble();
}
@Override
public String toString() {
return LambdaFunctionNode.this.toString();
}
}
}
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