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Implementation of a Prolog interpreter that works directly over the abstract syntax tree.

There is a newer version: 0.9.117

/*
 * Copyright The Sett Ltd, 2005 to 2014.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.thesett.aima.logic.fol.prolog.expressions;

import com.thesett.aima.logic.fol.NumericType;
import com.thesett.aima.logic.fol.Term;

/**
 * BinaryArithmeticOperator provides a base implementation for all two-place arithmetic operators on numeric arguments.
 * The {@link #getValue()} method invokes {@link #getValue()} on its arguments to recursively evaluate them, as they may
 * also be arithmetic operators or other {@link BuiltInExpressionOperator}s. It checks that the resulting arguments are
 * fully instantiated and numeric prior to calling the operators implementing {#evaluate} method to compute the result.
 *
 * 
 * CRC Card Responsibilities  Collaborations
 * 
 Ensure that both arguments evaluate to fully instantiated numbers.  {@link Term}, {@link NumericType}.
 * 
 Evaluate the arithmetic operator.
 * 
 *
 * @author Rupert Smith
 */
public abstract class BinaryArithmeticOperator extends BuiltInExpressionOperator
{
    /**
     * Creates a binary arithmetic operator on two arguments.
     *
     * @param name      The interned name of the operator.
     * @param arguments The operators arguments. There must be exactly two.
     */
    protected BinaryArithmeticOperator(int name, Term[] arguments)
    {
        super(name, arguments);

        // Ensure that there are exactly two argument.
        if (arguments.length != 2)
        {
            throw new IllegalArgumentException("BinaryArithmeticOperators must take exactly two arguments.");
        }
    }

    /**
     * Gets the actual value of a term, which is a numeric type equal in value to the arithmetic operator applied to its
     * arguments. This method checks that both arguments produce values which are fully instantiated and numeric when
     * their {@link Term#getValue()} methods are invoked.
     *
     * @return A numeric type equal in value to the the arithmetic operator applied to its arguments.
     */
    public Term getValue()
    {
        Term firstArgValue = arguments[0].getValue();
        Term secondArgValue = arguments[1].getValue();

        // Check that the arguments to operate on are both numeric values.
        if (firstArgValue.isNumber() && secondArgValue.isNumber())
        {
            return evaluate((NumericType) firstArgValue, (NumericType) secondArgValue);
        }
        else
        {
            return this;
        }
    }

    /**
     * Evaluates the arithmetic operator on its two numeric arguments.
     *
     * @param  firstNumber  The first argument.
     * @param  secondNumber The second argument.
     *
     * @return The result of performing the arithmetic operator on its arguments.
     */
    protected abstract NumericType evaluate(NumericType firstNumber, NumericType secondNumber);
}

Responsibilities	Collaborations *
Ensure that both arguments evaluate to fully instantiated numbers.	{@link Term}, {@link NumericType}. *
Evaluate the arithmetic operator. *