Turbo Prolog

5 Tutorial III: Turbo Prolog's
Relentless Search for Solutions
This chapter falls into two main parts. In the first, we examine in detail the process
Turbo Prolog uses when trying to match a goal with a clause. This process is called
unification and corresponds to parameter passing in other programming languages.
In the second part, you'll learn how to control Turbo Prolog's search for solutions of
goals. This will include techniques that make it possible for a program to carry out a task
which would otherwise be impossible, either because the search would take too long
or (less likely with Turbo Prolog) because the system would run out of free memory.
MATCHING THINGS UP:
THE UNIFICATION OF TERMS
Consider Program 13 in terms of the (external) goal
written_by(X,y).
1* Program 13 *1
domains
title, author symbol
pages integer
publication book(title,page)
predicates
written_by(author,publication)
long_novel(Title)
clauses
written_by(fleming,book("DR NO",210)).
written_by(melville,book("MOBY DICK",bOO))
long_novel(Title):-written_by(_,book(Title,Length)),
Length> 300.
When Turbo Prolog tries to fulfill the goal, it must try each of the clauses for the
predicate written-.by in turn, trying to get a match between the parameters X and Yand
the parameters in each clause for written_by. This term matching operation is called
unification.
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