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Core building blocks and API for the Metal library.

There is a newer version: 10.0.0

/*
 * Copyright 2013-2016 Netherlands Forensic Institute
 *
 * 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 io.parsingdata.metal.expression.value;

import static io.parsingdata.metal.Util.checkNotNull;

import io.parsingdata.metal.data.Environment;
import io.parsingdata.metal.data.ImmutableList;
import io.parsingdata.metal.encoding.Encoding;

/**
 * A {@link ValueExpression} that implements the Elvis operator:
 * ?:.
 * 
 * An Elvis expression has two operands: left and
 * right (both {@link ValueExpression}s). Both operands are
 * evaluated. The return value is a list with the size of the longest list
 * returned by the two evaluations. At each index, the value at that index in
 * the result returned by evaluating left is placed, except if it
 * does not exist or is {@link OptionalValue#empty()}, in which case the value
 * at that index in the result returned by evaluating right is placed there.
 */
public class Elvis implements ValueExpression {
    public final ValueExpression left;
    public final ValueExpression right;

    public Elvis(final ValueExpression left, final ValueExpression right) {
        this.left = checkNotNull(left, "left");
        this.right = checkNotNull(right, "right");
    }

    @Override
    public ImmutableList eval(final Environment environment, final Encoding encoding) {
        return eval(left.eval(environment, encoding), right.eval(environment, encoding));
    }

    private ImmutableList eval(final ImmutableList leftValues, final ImmutableList rightValues) {
        if (leftValues.isEmpty()) { return rightValues; }
        if (rightValues.isEmpty()) { return leftValues; }
        return eval(leftValues.tail, rightValues.tail).add(leftValues.head.isPresent() ? leftValues.head : rightValues.head);
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "(" + left + "," + right + ")";
    }
}