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Chapter Two: Syntax and Meaning of Prolog Programs

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Chapter two:2.1 Data objects

data objects

simple objects

constants

atoms numbers

variable

structures

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2.1 Data objects 2.1.1 Constants: atoms

String of letters, digits and the underscore character ‘_’ starting with a lower-case lettere.g. anna x25 x_34a x___y3 miss_Jones

String of special characterse.g. <----> ===> … ::= when using atoms of this form, be carefulbecause some of strings already havea predefined meaning e.g. ‘:-'

String of characters enclosed in single quotese.g. ‘Tom’ ‘tom’ ‘SarahJones’

The lexical scope of atom names is the whole program.

data objects

simple objects

constants

atoms numbers

variable

structures

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2.1 Data objects 2.1.1 Constants: numbers

Prolog is a primarily a language for symbolic and non numerical computation.

In symbolic computations, integers are often used, e.g. to count the numbers of items in a list; but there is less need for real numbers. Integer numbers

e.g. 1 133 0 -97 Real numbers

e.g. 3.14 -0.0035 100.2

data objects

simple objects

constants

atoms numbers

variable

structures

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2.1 Data objects 2.1.2 Variables

Variables are strings of letters, digits and underscores characters, starting with upper-case letter or an underscore.e.g. X Result Object2 _23 Shopping_list _ (the anonymous variable)

The lexical scope of variable names is oneclause except the anonymous variable; it signifies new variable each time itoccurs even in the same clause.e.g.

somebody_has_child:-parent(_,_).somebody_has_child:-parent(X,Y).somebody_has_child:-parent(X,X).

data objects

simple objects

constants

atoms numbers

variable

structures

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2.1 Data objects 2.1.3 Structures

Structures are objects that have several components which can be structures themselves.e.g. date (1, may, 2001)

to represent any day in may; day is variable date (Day, may, 2001)

All structures can be pictured as tree.

Each functor is defined by name and arity (#of arguments)

functor arguments (all are constants)

date

may1 2001

data objects

simple objects

constants

atoms numbers

variable

structures

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2.1 Data objects 2.1.3 Structures

Example: how structures can be used to represent the following geometric objects: A point in 2 dimensional space A line segment A triangle (a + b) * (c - 5)Draw the tree structures thatcorrespond to them.

data objects

simple objects

constants

atoms numbers

variable

structures