/*
 * Name: Mike Cifelli
 * Course: CIS 443 - Programming Languages
 * Assignment: Lisp Interpreter 1
 */

package eval;

import parser.*;

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

    public SExpression call(Cons argList) {
        // make sure we have received at least one argument
        if (argList.nullp()) {
            Cons originalSExpr = new Cons(new Symbol("/"), argList);

            throw new RuntimeException("too few arguments given to /: " +
                                       originalSExpr);
        }

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

        // make sure that the first argument is a number
        if (argFirst.numberp()) {
            LispNumber num1 = (LispNumber) argFirst;

            if (argRest.nullp()) {
                // there is only one argument, so return the multiplicative
                // inverse of the number
                return new LispNumber(1 / num1.getValue());
            }

            SExpression argSecond = argRest.getCar();

            // make sure that the next argument is a number as well
            if (argSecond.numberp()) {
                LispNumber num2 = (LispNumber) argSecond;
                LispNumber quotient = new LispNumber(num1.getValue() /
                                                     num2.getValue());
                SExpression argCddr = argRest.getCdr();

                if (argCddr.consp()) {
                    return call(new Cons(quotient, argCddr));
                }

                return quotient;
            }
                
            throw new RuntimeException("/: " + argSecond + " is not a number");
        }

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

}