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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchlib.rankingexpression.rule;
import com.google.common.collect.ImmutableList;
import com.yahoo.searchlib.rankingexpression.evaluation.Context;
import com.yahoo.searchlib.rankingexpression.evaluation.MapContext;
import com.yahoo.searchlib.rankingexpression.evaluation.Value;
import java.util.Collections;
import java.util.Deque;
import java.util.List;
import java.util.function.DoubleBinaryOperator;
import java.util.function.DoubleUnaryOperator;
/**
* A free, parametrized function
*
* @author bratseth
*/
public class LambdaFunctionNode extends CompositeNode {
private final ImmutableList<String> arguments;
private final ExpressionNode functionExpression;
public LambdaFunctionNode(List<String> arguments, ExpressionNode functionExpression) {
// TODO: Verify that the function only accesses the given arguments
this.arguments = ImmutableList.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 String toString(SerializationContext context, Deque<String> path, CompositeNode parent) {
return ("f(" + commaSeparated(arguments) + ")(" + functionExpression.toString(context, path, this)) + ")";
}
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();
}
/** 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);
return new DoubleBinaryLambda();
}
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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