transcendental-lisp/src/eval/LIST.java

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

package eval;

import parser.*;
import sexpression.Cons;
import sexpression.Nil;
import sexpression.SExpression;

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

    /**
     * Places the given S-expression into a list.
     *
     * @param sexpr
     *  the S-expression to be placed into a list
     * @return
     *  a list with <code>sexpr</code> as the car and NIL as the cdr.
     */
    public static Cons makeList(SExpression sexpr) {
        return new Cons(sexpr, Nil.getUniqueInstance());
    }

    public Cons call(Cons argList) {
        if (argList.nullp()) {
            // return NIL if there were no arguments passed to LIST
            return Nil.getUniqueInstance();
        }

        SExpression argCar = argList.getCar();
        Cons argCdr = (Cons) argList.getCdr();

        return new Cons(argCar, call(argCdr));
    }

}