How To ... > Use PML with Prolog

There are many Prolog tutorials and examples on the web using proof traces to describe how Prolog works. However, you may not be able to "play" with the proofs or get additional information about proof-related information such as resolution by browsing the these proofs. With the help of few Inference Web tools you may be able to change your way of using and publishing proofs on the web. The Prolog code used distributed in this page was tested on SWI-Prolog. If you know that it works on other versions of Prolog or you have an alternative code for other version of Prolog, please let us know.

1. Install IWToolkit (you will need a java virtual machine to run IWToolKit)
2. Save pml.pl in your Prolog home directory
3. Enter in Prolog by typing pl and load pml.pl by typing [pml]. (including the period at the end).

Now you are ready to use the PML's interface to Prolog. pml.pl defines the following three predicates:

1. why_all\1 : Use why_all(goal) to bring up explanatory proofs for all possible ways of satisfying goal
2. why\1 : Use why(goal) to bring up an explanatory proof for the first way of satisfying goal.
3. why\2 : Use why(goal, n) to bring up an explanatory proof for the first n ways of satisfying goal.

In order to test the working of the tool on a simple test case:

1. Save testcase.pl in your Prolog home directory
2. Enter in Prolog by typing pl in you operating system prompt.
3. Load pml.pl by typing [pml]. (including the period at the end).
4. Load testcase.pl by typing [testcase]. (including the period at the end).
5. Now you can try any of the following:
   • why_all(p(X)).
   • why(factorial(3, 6)).
   • why(factorial(3, X)).
   • why_all(factorial(3, X)).
   • why(f(X)).
   • why_all(f(X)).

Note: the pml.pl code above is quite simple and there are many things we can do improve its use of PML such as: