Slide 17.1.1 Normal Order(Lazy) Evaluation Over the past few lectures, we have been looking at evaluation especially how to implement eval and apply in a anguage such as Scheme, in order to define a language. What we have seen is that by creating, or specifying, eval and its associated procedures, we actually define the semantics of the

signment exp en ((definition? exp)(eval-definition exp env)) ((if? exp)(eval-if exp env)) ((lambda? exp) (make-procedure (lambda-parameters exp)(lambda-body exp) env)) ((begin? exp)(eval-sequence (begin-actions exp)env)

Slide 16.1.1 Building up a language Last time, we completed building our evaluator. And as you saw, we slightly misled you. We started off saying we were going to user Scheme's lexical analyzer and parser, but then build our own evaluator, which we did initially for arithmetic

1. Arithmetic calculator 6 (define (eval exp) 8 ((number? exp) exp) ((sum? exp (eval-sum exp))

Slide 15.6.1 The next stage in the evolution of our evaluator is to pull the 5. Environment as explicit parameter environment out as an explicit parameter. Up until now we could rely on just having a single environment in which to store (eva1'(pus*64)) bindings for variables. It made sense to have a global

Slide 15.1.1 Why do we need an interpreter? Our goal over the next few lectures is to build an interpreter which in a very basic sense is the ultimate in programming, since doing so will allow us to define our language

Slide 14.4.1 Cleaning up some details of our implementation So we have seen a first pass at building an object-oriented tem, using Scheme as the base. There are a few details that The need for self-reference

Slide 14.1.1 Elements of ooP Last time we introduced the idea of object oriented systems Today, we want to build on those basics, looking at how we can expand object-oriented systems to deal with hierarchies of objects, to leverage the commonality of methods between

The role of abstractions In this lecture, we are going to look at a very different style of creating large systems, a style called object oriented programming. This style focuses on breaking systems up in a different manner than those we have seen before To set the stage for this, we are first going to return to the notion of

luse this is the central part of the environment model, let's look in very painful detail at an example of an evaluation. In (square 4)I g particular, let's look at the evaluation of (square 4)with x;10 respect to the global environment. Here is the structure we start