Closure.java

// Closure.java -- the data structure for function closures

// Class Closure is used to represent the value of lambda expressions.
// It consists of the lambda expression itself, together with the
// environment in which the lambda expression was evaluated.
// The method apply() takes the environment out of the closure,
// adds a new frame for the function call, defines bindings for the
// parameters with the argument values in the new frame, and evaluates
// the function body.
class Closure extends Node {

    private Node fun;		// a lambda expression
    private Environment env;	// the environment in which the function
    // was defined

    public Closure(Node f, Environment e) {
        fun = f;
        env = e;
    }

    public Node getFun() {
        return fun;
    }

    public Environment getEnv() {
        return env;
    }

    // TODO: The method isProcedure() should be defined in
    // class Node to return false.
    @Override
    public boolean isProcedure() {
        return true;
    }

    @Override
    public void print(int n) {
        // there got to be a more efficient way to print n spaces
        for (int i = 0; i < n; i++) {
            System.out.print(' ');
        }
        System.out.println("#{Procedure");
        fun.print(n + 3);
        for (int i = 0; i < n; i++) {
            System.out.print(' ');
        }
        System.out.println('}');
    }

    @Override
    public Node apply(Node args) {
        //ie (lambda (foo x) (...))
        Node params = fun.getCdr().getCar().getCdr(); //cdadr(fun);
        Node body = fun.getCdr().getCdr(); //cddr(fun);
        //define params
            //traverse args (value) and params (variable names) at the same time and define
        while((args != null) && !args.getCar().isNull()){
            env.define(params.getCar(), args.getCar());
            params = params.getCdr();
            args = args.getCdr();
        }
        //eval body with newly defined variable

        return body.eval(env);
    }
    
}