Preface to the Fifth Edition
Since the previous edition
of Programming
in
Prolog,
the Prolog language has
been standardised by the International Organization for Standardization (ISO). Al-
though not all Prolog systems conform to the new standard, we
felt
it was necessary
to take the opportunity to update this book in accordance with the standard. We have
also introduced some new material, clarified some explanations, corrected a number
of minor
errors,
and removed appendices about Prolog systems that are now obsolete.
This book can serve several purposes. The aim
of
this book is not to teach the
art
of
programming as such. We feel that programming cannot be learned simply by
reading a book or by listening to a lecturer. You've got to do programming to learn it.
We hope that beginners without a mathematical background can learn Prolog from
this book, although in this case we would recommend that the beginner is taught by
a programmer who knows Prolog, as part
of
a course that introduces the student to
programming as such. It is assumed that beginners can obtain the use
of
a computer
that has a Prolog system installed, and that they have been instructed in the use of
the computer. Experienced programmers should not require extra assistance, but we
hope they will not be dismayed at our intention to restrain mathematical elaboration.
In our experience, novice programmers find that Prolog programs seem to be
more comprehensible than equivalent programs in conventional
languages.
However,
the same people tend not to appreciate the limitations that conventional languages
place on their use
of
computing resources. On the other hand, programmers experi-
enced in conventional languages are better prepared to deal with abstract concepts
such as variables and control flow. But, in spite
of
this prior experience, they may
find Prolog difficult to adapt to, and they may need a lot
of
convincing before they
consider Prolog a
useful
programming tool.
Of
course, we know
of
many highly ex-
perienced programmers who have taken up Prolog with much enthusiasm. However,
the aim
of
this book is not to convert, but to teach.
Programming in Prolog can be a useful companion to two other books. The
beginner might use Programming in Prolog as a tutorial preliminary to the more
