transcendental-lisp/src/function/builtin/MULTIPLY.java

package function.builtin;

import java.math.BigInteger;

import function.LispFunction;
import sexpression.*;

/**
 * <code>MULTIPLY</code> represents the '*' function in Lisp.
 */
public class MULTIPLY extends LispFunction {

    public LispNumber call(Cons argList) {
        if (argList.nullp()) {
            return new LispNumber(BigInteger.ONE);
        }

        SExpression argFirst = argList.getCar();
        Cons argRest = (Cons) argList.getCdr();

        if (argFirst.numberp()) {
            LispNumber num1 = (LispNumber) argFirst;
            LispNumber num2 = call(argRest);

            return new LispNumber(num1.getValue().multiply(num2.getValue()));
        }

        throw new RuntimeException("*: " + argFirst + " is not a number");
    }

}