Languages & Environments

Recursion

ancestor_of(X,Y):- parent_of(X,Z), ancestor_of(Z,Y)

This reads as 'X is an ancestor of Y if X is a parent of Z and Z is an ancestor of Y'. Recursion is evident here as the rule ancestor_of(X,Y) calls itself within the rule definition – ancestor_of(Z,Y).

Activity: PROLOG

facts describe who is warm, who is fed and who is cold. There are two simple rules to

Match the answers to the following queries:

a) Yes

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a) Yes

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a) Yes

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a) X = jim

b) X = fred

c) X = justin

d) X = jim, X = Justin

Object-orientated languages

Procedural languages rely on the process of passing data from one procedure to another. Procedures and the code within them exist independently of the data. They simply access data deemed relevant by the programmer as and when necessary. The data used is separate from the code.

However, object-oriented languages treat data and code as part of the same object. Firstly a class is created. A class acts as a template for an object and classes are examined in more detail later in this section. Objects are created within a class and will contain code and the data that the code requires. Data and code is not held separately. The name given to the concept of an object containing both the code and its related data is called 'encapsulation'.

In our world there are many objects such as cars, boats, buses, doors etc. To think of objects in this way is a good starting point. An object such as a train will have a set of attributes.