/*
 * Copyright 2009-2010 Yuichiro Moriguchi
 *
 * 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 net.morilib.lisp.compare;

import net.morilib.lisp.Cons;
import net.morilib.lisp.Datum;
import net.morilib.lisp.Environment;
import net.morilib.lisp.LispMessage;
import net.morilib.lisp.Procedure;
import net.morilib.lisp.Scheme;
import net.morilib.lisp.subr.BinaryArgs;
import net.morilib.lisp.subr.UnaryArgs;

/**
 *
 *
 * @author MORIGUCHI, Yuichiro 2011/07/22
 */
public class PairCompareCar extends UnaryArgs {

	//
	private static class Comp extends BinaryArgs {

		//
		private Procedure proc;

		//
		private Comp(Procedure proc) {
			super("compare-car-procedure");
			this.proc = proc;
		}

		/* (non-Javadoc)
		 * @see net.morilib.lisp.subr.BinaryArgs#execute(net.morilib.lisp.Datum, net.morilib.lisp.Datum, net.morilib.lisp.Environment, net.morilib.lisp.LispMessage)
		 */
		@Override
		protected Datum execute(Datum c1a, Datum c2a, Environment env,
				LispMessage mesg) {
			if(!(c1a instanceof Cons)) {
				throw mesg.getError("err.require.pair", c1a);
			} else if(!(c2a instanceof Cons)) {
				throw mesg.getError("err.require.pair", c2a);
			} else {
				return Scheme.callva(proc, env, mesg,
						((Cons)c1a).getCar(), ((Cons)c2a).getCar());
			}
		}

	}

	/* (non-Javadoc)
	 * @see net.morilib.lisp.subr.UnaryArgs#execute(net.morilib.lisp.Datum, net.morilib.lisp.Environment, net.morilib.lisp.LispMessage)
	 */
	@Override
	protected Datum execute(Datum c1a, Environment env,
			LispMessage mesg) {
		if(c1a instanceof Procedure) {
			return new Comp((Procedure)c1a);
		} else {
			throw mesg.getError("err.require.procedure", c1a);
		}
	}

}
