Chapter 29 Declarative Programming

Question 1

What is the difference between imperative and declarative languages?

Answer 1

In imperative programming languages the programmer writes a sequence of statements that reflect how to solve the problem while is declarative the programmer writes a sequence of statements that reflect what the problem is and it is up to the logic programming system to work out how to get the answer.

Question 2

Which are the three basic constructs of Prolog? Give an example to each one of them.

Answer 2

Facts: capitalCities(budapest).
Rules: grandparent(A, B) :- parent(A, P), parent(P, B).
Queries: citieInCountry(budapest).

Question 3

What are clauses?

Answer 3

Clauses are facts and rules.

Question 4

What data type does a prolog have?

Answer 4

Prolog has a single data type, called ‘term’.

Question 5

What can a term be?

Answer 5

A term can be an atom, a general-purpose name with no inherent meaning that alway starts with a lower case letter
A term can be a number, integer or float (real)
A term can be a variable, denotated by an identifier that starts with a capital letter or an underscore (_)
A term can be a compound term, a predicate, consisting of an atom and a number of arguments in parantheses

Question 6

How to test the fact capitalCity(paris).?

Answer 6

capitalCity(paris).
You write this first in the Prolog environment
Then you write this in the SWI-Prolog
The output should be true.

Question 7

Where is the variable in cityInCountry(berlin, Country).?

Answer 7

The Country is the variable right after berlin,.

Question 8

What happens if you had the program cityInCountry(berlin, germany). in the Prolog environment and wrote cityInCountry(berlin, Country). in the SWI Prolog.

Answer 8

The output would be

Country = germany

Question 9

Give an example of anonymus variable

Answer 9

Prolog environment:
ingredient(tagine, tomato, 100).
SWI Prolog:
ingredient(tagine, Ingredient, _).
Output
Ingredient = tomato 
'The amount won't be outputed

Question 10

Give an example of a rule.

Answer 10

parent(fred, jack).
parent(fred, alia).
parent(fred, paul).
parent(dave, fred).
grandparent(A, B) :- parent(A, P), parent(P, B).

Question 11

How do you debug your code in Prolog environment?

Answer 11

To debug the code you go to debug, graphical debugger than write trace. the part of the code you want and than just push the space button in the debugger program to see the program unfold

Question 12

Where does recursion occur?

Answer 12

Recursion occurs where a rule is defined by itself or more precisely a rule uses itself as a sub-goal

Question 13

What is the head and tail in a list?

Answer 13

The head is the first item and the tail is the rest of the list.

Question 14

Write or say an example of a list.

Answer 14

Prolog environment
showHeadAndTail([fred, jack, emma], head, tail).
SWI Prolog
?- showHeadAndTail([H|T], head, tail).
H = fred,
T = [jack, emma].