Turbo Prolog

domains
global domains
database
predicates
global predicates
goal
clauses
Table 11-1 Keyword Contents
Zero or more domain declarations.
Zero or more domain declarations.
Zero or more database predicate declarations.
One or more predicate declarations.
Zero or more predicate declarations.
Goal.
Zero or more clauses (facts or rules).
Usually, a program will require at least predicates and clauses sections. For large
programs, a domains section will help you economize on code for the same reason
that types are used in Pascal. (This is a system requirement if any of the objects in a
Turbo Prolog program belong to domains of a non-standard type).
For modular programming, the keywords domains and predicates can be prefixed
with the word global, indicating that the subsequent domain declarations or predicate
declarations affect several program modules globally (modular programming is discussed
on page 152).
A program can contain several domains, predicates, or clauses sections, provided
the following restrictions are observed:
• A program section must be prefaced with the corresponding keyword (domains,
database, predicates, clauses, or goal).
• Only one goal must be met during compilation.
• All clauses that describe the same predicate must occur one after the other.
• At most, one global predicates section may be encountered during compilation,
and then only if there have been no ordinary predicates declarations earlier.
• Sections containing database predicates must occur before all global and ordinary
predicates declarations.
Domain Declarations
A domains section contains domain declarations. Four formats are used:
I. name = d
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This declaration declares a domain, name, which consists of elements from a standard
domain type, d, which must be either integer, char, real, string, or symbol.
This declaration is used for objects that are syntactically alike but are semantically
different. For instance, NoOfApples and HeightlnFeet could both be represented as
integers and thus be mistaken for one another. This can be avoided by declaring
two different domains of integer type
apples,height = integer
This allows Turbo Prolog to perform domain checks to ensure that apples and
heights are never inadvertently mixed.
Turbo Prolog Owner's Handbook