| Title: Scope
Description: None
Copyright (c) 1999 Steven J. Metsker.
Copyright (c) 2001 The Open For Business Project - www.ofbiz.org
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A scope is a repository for variables. A dynamic rule has
a scope, which means that variables with the same name
are the same variable. Consider a rule that describes
big cities:
bigCity(Name) :- city(Name, Pop), >(Pop, 1000000);
This example follows the Prolog convention of using
capitalized words for variables. The variables Name
and Pop have scope throughout the rule.
The bigCity rule proves itself by finding
a city and checking its population. When the city
structure binds with a city fact in a program, its
variables take on the values of the fact. For example,
city might bind with the fact
city(bigappolis, 8733352) . Then Name
and Pop will bind to the values "bigappolis"
and 8733352.
When the comparison proves itself, it will compare
Pop to 1000000. This is the same variable as
Pop in the city structure of the rule.
With this successful comparison, the rule completes a
successful proof, with Name bound to
"bigappolis".
author:
Steven J. Metsker
version:
1.0 |
