Frequently Asked Questions

This page contains some frequently asked questions, together with their answers: please check these to see if they solve your problem.


The following questions have been asked about running WIN-PROLOG:

Q: When I try to "assert" or "retract" programs in WIN-PROLOG, I get a "Predicate Protected" error. Why does this happen?
A: The "Predicate Protected" error is due to a feature of modern Prologs: if you load a file containing a definition for a relation, say "foo/1", this is treated as "static" code. You can "abolish" the entire relation, or reload the file, but you cannot assert to or retract from foo/1 unless you have first declared it "dynamic". To do this, simply add a "dynamic" statement at the top of the appropriate source file, for example:
        :- dynamic foo/1.
        foo( 123 ).
        bar( 456 ).
If you were to load this file, you would be able to assert to and retract from foo/1, but not bar/1.

Downloaded Software

The following questions have been asked about downloaded software:

Q: When I download software from the LPA website, I get a single file with a ".ZIP" extension: what is this, and how do I use it?
A: "ZIP" files are simply files that contain a number of other files and even directories (folders) in a compressed format that makes them faster to download and easier to manage. There are many software programs available which can create and unpack ZIP files, and we recommend the original program, PKZIP 2.50. You can obtain a shareware copy of this program directly from the Pkware website, at
Q: I requested a copy of the WIN-PROLOG Free Trial, but was told how to get it. When I try again, I'm told I've already got a copy. Why?
A: The WIN-PROLOG Free Trial systems relies on you typing in a valid name and email address into a web form, optionally with some other information about yourself; you then "Submit" this information to the LPA web server. When the web server receives this request, it first checks its records to see whether you've already had a copy, and if not, then emails you the details of how to download your personalised copy.

If you mistyped your email address (or entered a fake one...), then you will never receive the information about how to download your copy of the WIN-PROLOG Free Trial. Incredibly, every day, 3-4 people submit false names like "sjkdfh sldhjf" and email addresses like "dklg@qwye.cvb", and then wonder why they don't get their free trial software!

If you made a genuine mistake when typing in your name or email address, or if your email notification was lost for some other reason, please email the webmaster explaining what happened, and we will arrange a new copy for you. Please click on the "Information" tab for contact details.