Runner.java

// Kimberley Ni and Eylul Oktay

public class Runner {
    Dictionary dict;

    public Runner() {
        dict = new Dictionary();
    }

    /*
	 * Given an expression tree, this returns the ran expression.
	 */
    public static Expression run(Expression exp) {
        //System.out.println(exp);
        Expression before = exp.copy();
        //System.out.println(before);
        Expression ran = runCycle(exp, false);
        //System.out.println(ran);
        while (!(before.equals(ran))) {
            before = ran.copy();
            ran = runCycle(ran, false);
            //System.out.println(ran);
        }

        return Dictionary.getKey(ran);
    }

    public static Expression runCycle(Expression exp, Boolean ranRedex) {
        // MAKE BASE CASES HERE
        if (exp.isSimple() || ranRedex == true) {
            return exp;
        }

          // If the expression is an Application
        if (exp instanceof Application) {
            Application app = (Application) exp;
            Expression left = app.getLeft();
            Expression right = app.getRight();

            // If the left side of the application is a Function, perform beta reduction
            if (left instanceof Function) {
                Function func = (Function) left;
                Expression body = func.apply(right); // Apply the argument to the function
                // Recursively run the resulting expression
                return runCycle(body, true);
            } else {
                // Otherwise, recursively run the left and right sides
                Expression leftCopy = left.copy();
                Expression leftAttempt = runCycle(left, ranRedex);
                if (!(leftCopy.equals(leftAttempt))) ranRedex = true;
                return new Application(leftAttempt, runCycle(right, ranRedex));
            }
        } else {
            Function func = (Function) exp;
            Variable param = func.getParameter();
            Expression body = func.getBody();
            return new Function(param, runCycle(body, ranRedex));
        }
    }
}