CS 135 (Module 4: Simple Data)

What is a Boolean value and what functions produce it?

A boolean value is a true or false statement that is created by functions <, >, <=, >= and =

What is a predicate?

A function which produces a Bool is a predicate. Many predicate names in Racket ends with ?.

What is a way we can write our own predicate?

(define (can-vote? age)
(>= age 18)

What are string predicates?

Non-numeric types also have predicates. These predicates consume strings and are later used with on work with strings. (Ex: string=? "pearls" gems") -> false)

Describe conditional expressions.

Sometimes expressions should take one value under some conditions, and other values under other conditions.

What do conditional expressions do?

They are the key tool in Racket that allows us to vary the execution of the program depending on the condition that it encounters.

In what form are conditional expressions used in?

The special form cond.

Each arguments is a ____ pair.

question/answer

The ___ is a Boolean expression.

question

The ___ is a possible value of the conditional expression.

answer

How do we evaluate a cond?

We evaluate it by considering the question/answer pairs in order, top to bottom. When doing that, we evaluate the question. If the question evaluates to true, the whole cond produces the corresponding answer.

What happens if none of the questions evaluate to true?

An error occurs.

How do we fix the error?

We could use a question which always evaluates to true, which is used by else.

What is a trace?

The way we evaluate a program through a sequence of substitutions following rules we've defined.

What special forms do we use to combine predicates?

We use and, or, and the function not. These all consume and produce Bool values.

___ has value ___ when all of its arguments have value ___ and ___ otherwise.

and, true, true, false

___ produces ___ if at least one of its arguments is ___ and ___ otherwise.

or, true, true, false

___ produces ___ if its argument is ___, and ___ if its argument is ___

not, true, false, false

(and false ...) ->

false

(and true ...) ->

(and ...)

(and) ->

true

(or true ...) ->

true

(or false ...) ->

(or ...)

(or) ->

false

Tests, including examples, that have been defined before the body of the function was written are known as:

Closed-box texts because they are not based on details of the code.

Test that may depend on the code, for example, to check specific answers in conditional expressions are known as:

Open-box tests.

What is a symbol?

Racket allows one to define and use symbols with meaning to us. A symbol is defined using an apostrophe or 'quote': 'CS135

How can symbols be compared?

Using the predicate symbol=?

What is a character?

A character is most commonly a printed letter, digit, or punctuation symbol. a, G, ., + and 8 are all characters.

What are strings?

Strings are sequences of characters between double quotes. Examples: "pink" and "My hair is black"

What type of data are strings?

Strings are really compound data. (a string is a sequence of characters)

What is the contract for:
1. Numbers:
2. Integers:
3. Natural Numbers:
4. Booleans:
5. Characters:
6. Strings
7. Symbols
8. Values of any type

1. Num
2. Int
3. Nat
4. Bool
5. Char
6. Str
7. Sym
8: Any