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MASSACHVSETTS INSTITVTE OF TECHNOLOGY epartment of Electrical Engineering and Computer Se lence 001--Structure and Interpretation of Computer Programs Spring Semester, 2005 Quiz I- Sample Solutions

Evaluation and universal machines The Eval/Apply Cycle What is the role of evaluation in defining a language? Eval and Apply execute a cycle that unwinds our abstractions Reduces to simple applications of built in

The 6.001 Lazy Meta-Circular Evaluator The Core Evaluator (define (l-eval exp env) (cond ((self-evaluating? exp) exp) ((variable? exp)(lookup-variable-value exp env)) ((quoted? exp)(text-of-quotation exp)) ((assignment? exp)(eval-assignment exp env)) ((definition? exp)(eval-definition exp env)) ((if? exp)(eval-if exp env))

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

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

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 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

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

Slide 12.1.1 In the last lecture, we introduced mutation as a component of 6001s|cP our data structures We saw for example that set was a Environment mode way of changing the value associated with a variable in our system, and we saw that set-car! and set-cdr! were ways of changing the values of parts of list structure Now, several important things happened when we introduced