1.0 Introduction

Question 1

What does {…} mean?

Answer 1

Used for procedure- and function calls

Question 2

What des {Browse X} do?

Answer 2

Open browser window with content of X

Question 3

Describe an Oz variable

Answer 3

Variables has 2 components, an identifier and a store variable.

Identifier: Name, start with uppercase letter

Store variable: Part of system’s memory. Declare creates a new store variable, and makes identifier point to it.

Must be declared.

Values are bound to variables. Once a variable is assigned a value, it can not change.

declare
A = 10

Variables later in the program can have the same name as a previous variable. In this case, the old value will be overwritten, and cannot be accessed again.

Variables/calculations done with the previous variable-value will remain the same. This is because the identifier just refers to a new store variable, not overwriting the previous one.

Question 4

Describe an Oz function?

Answer 4

declare
fun {FunName X}

declare: Creates new variable FunName
fun: Statement, defines a function
FunName: Bound to this function

Question 5

What is functional abstraction?

Answer 5

When functions are used to define other functions.

declare
fun {Fun2 X Y}
{Fun1 X Y}
end

Question 6

Define lists in OZ

Answer 6

List contains 2 things:
- Head-element
- reference to the rest of the list (Tail-list)

Can create a list by adding Head-elements:
a = nil
b = 1|a
c = 2|b

Fetch list components:
L.1: Gives list head-element
L.2: Gives reference to rest of the list

Question 7

What is consing?

Answer 7

Cons (or a pair): The link H|T

Consing: Creating a new link

If T is a list. Consing H and T creates the new list H|T

Question 8

Describe Oz pattern matching

Answer 8

case List of H|T then S end

case: Declares 2 local variables and binds them to the Head and Tail of the list.

case decomposes the list List based on the pattern H|T

Question 9

What is language semantics?

Answer 9

A mathematical model of the operations of a prorgamming language, defining what the operations should do

Question 10

What is program specifications?

Answer 10

What a program should do.

The mathematical definitions of input provided to the program and output it calculates..

Question 11

How to declare local variables within if-else statements?

Answer 11

if condition then
// block
else L in
L = 5
end

Question 12

What is a program’s time complexity?

Answer 12

Execution time as function of input size, up to a constant factor.

Question 13

What is lazy evaluation?

Answer 13

Only doing a calculation when the result is needed.

fun lacy {Count N}
N | {Count N+1}
end
lazy: function will only be evaluated when needed

Question 14

What does <future> mean when returned by a Browse function?</future>

Answer 14

That the variable has a lazy function attached to it.

Question 15

How can you access values returned from a lazy function?

Answer 15

Values will only be calculated when needed.

L = {Count N} // Here Count is a lazy function

{Browse L}: returns L<future></future>

{Browse L.1}: returns first element of L

case L of A|B|C|_ thn {Browse A + B + C} end

Here the first three values of L is needed, therefor they are calculated

Question 16

What is higher order programming?

Answer 16

Functions that takes other functions as argument

declare
fun {HigherOrder Op X}
{Op X}
end

Question 17

What is concurrency?

Answer 17

When programs consist of several independent activities that operate at their own pace. The programmer specifies communication between these.

Question 18

What is a thread, and how are they created?

Answer 18

An executing program.

Program can contain multiple threads.

thread
{Browse ‘hello’}
end

Question 19

What is dataflow behaviour?

Answer 19

If a function tries to access a variable that is not yet bound, the program waits until this variable gets bound, maybe by another thread running.

Question 20

What is dataflow concurrency?

Answer 20

Programs with dataflow behaviour will always produce the same results, however operations and bounding is partitioned between threads.

As long as the same operations are performed, with the same arguments, their behaviour remains the same.

Question 21

What is an object and an objects interface?

Answer 21

A function with internal state.

The interface of an object is the functions defined within it.

declare
local C in
C = 1
fun {Fun1}
return 1
end
fun {Fun2}
return 2
end
end

Question 22

What is the difference between object based- and object oriented programming?

Answer 22

Both use classes and objects, but object-oriented also implement inheritance.

Question 23

What is nondeterminism?

Answer 23

Threads operate independently. Because of this they may operate in different orders in different program runs, leading to different program outputs (race condition)

Question 24

What does it mean that threads are interleaving?

Answer 24

They take turn executing a little bit of their programs at the time. Meaning, when one thread is scheduled, it may not run to completion, when the next is scheduled.