CIS 352 — SPRING 2009

Exam 2: Scope and Practice

Version 2 — 24 March 2009

When, Where, and How

When: Thursday, March 26
Where: in class
How: Closed book, closed notes.

Coverage

Through Chapter 2 of Dybvig and Chapters 1, 2, and 3 of EOPL.

You should be familiar with all the topics from Exam 1.
Terms.
Know the following terms, all of which are in the index of the text or in notes I've provided. Be able to define them and apply them (or give an example). For example, be able to define what a bound variable is and to pick out the bound variables in some Scheme code.
- abstract syntax
- actual parameter
- BNF
- bound variable
- closure
- concrete syntax
- contours
- denoted value
- defined language
- defining language
- dynamic scoping
- environment
- expressed value
- formal parameter
- free variable
- higher-order procedure
- hole in a scope
- lexical address
- lexical scoping
- nested region
- shadowed variables
- syntactic category
Be prepared for the following sorts of questions.
- What does the following code return when
  Explain your answers.
  Simple example. Consider:
```
   let x = 1 in
     let p = proc(y) +(x,y) in
       let x = 100 in
         p(0);
```
  1. Under lexical scoping this returns: 1.
  2. Under dynamic scoping this returns: 100.
- What value does (foo 17) return? Explain your answer.
- Describe the closure for the following procedure X.
- Define a datatype to represent X.
  Use a given datatype to do X.
  Simple example. Consider:
```
  (define-datatype bintree bintree?
     (leaf (label string?))
     (branch (label string?) (left bintree?) (right bintree?)))
```
  Define a procedure preorder that given a bintree argument, returns a list of all the labels in the tree in preorder.
- Given a BNF definition for concrete syntax, a define-datatype definition for abstract syntax, and a specific piece of concrete syntax, draw the corresponding abstract-syntax tree.
- Write a Scheme procedure to do X. (Where X is something not too involved.)
  For samples, see the problems in EOPL chapter 1.
- Given the following Scheme definitons, what are the values of the following expressions.
  
  For an example, see Question 1 of Exam 1.
- Add the following feature to the LETREC interpreter, where the question provides the concrete and abstract syntax for the feature and also the code for LETREC's value-of procedure.
  Simple examples.
  1. a primitive function max such that max(exp1,exp2) returns the maximum of the values of exp1 and exp2.
  2. a case expression similar to Java's.

Practice

Last year's Exam 2 with sample solutions.
Note: Questions 3a and 4 on last year's Exam 2 concern matterial we are not covering this year.

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Jim Royer /