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Frequently Asked Questions (FAQ)

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

    Running WIN-PROLOG

    The following questions have been asked about running WIN-PROLOG:
    Q: When I try to install WIN-PROLOG 4.100, I get a "String Too Long" error: what's this all about?
    A: This error occurs on certain Windows 2000 systems, where one or more of the "Environment Variables" has a value that exceeds 512 characters in length: the most common case is the "PATH" variable. This problem has been completely overcome in WIN-PROLOG 4.200, and we recommend you to upgrade your system if you experience this problem.
    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.
    Q: When I try to run WIN-PROLOG, I get a error message about something to do with the "wrong version of CTL3D32.DLL". What's this all about?
    A: The "CTL3D" family of DLLs is a minefield, causing endless problems with software installations. The problem arises from the fact that Microsoft never quite standardised this DLL, and released a number of "unofficial" versions which remain in circulation.

    Prolog uses the Microsoft file "CTL3D32.DLL" to provide grey, 3D-look dialogs and controls, but if your Windows system contains a non-standard version (often this will be a result of installing other third-party software), Windows may complain. If this happens, you have two choices. The first is to stop Prolog from using CTL3D completely by adding the "/Z1" switch to the command line, for example:

    	pro386w /z1
    Any dependency on CTL3D32.DLL has been completely removed in WIN-PROLOG 4.200, and we recommend you to upgrade your system if you experience this problem.

    Downloaded Software

    The following questions have been asked about downloaded software:
    Q: I've downloaded a copy of the WIN-PROLOG 4.200 Free Trial, but all it does is display a sequence of license screens, before quitting. Why don't I get to use Prolog?
    A: The chances are that you forgot to preserve directories (folders) when you "unzipped" your copy of the software. Using the recommended PKUNZIP 2.50 unzipper, for example, you must specify the "-d" switch:

    	C> pkunzip -d abcd1234
    where "abcd1234.zip" is the name of your file (these names are assigned randomly). If you are using another unzip program, make sure you select its option to preserve directories or folders.
    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 www.pkware.com.
    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.