Tcl/Tk Logicbase Query Sample

This sample illustrates a simple Tcl/Tk interface that can
be used to query a logicbase, where a logicbase is a collection
of predicates designed to be queried like a database.

It illustrates:
   - setting up a GUI from a logic program, using Tcl/Tk, and
   - making logicbase queries from Tcl/Tk.

Use File/Open to open one of the sample logicbases, either
gene.lb or pets.lb.

Enter a query in the data entry box, such as:
   pet(Type, Name)
for pets.lb, or
   sister(X, Y)
for gene.lb.

More complex queries can be used as well, such as:
  pet(Type, Pet1), pet(Type, Pet2)
to find all the pets of the same type.

Select either button:
   'Once' - Retrieve a single answer to the query, with no backtracking.
   'First' - Retrieve the first answer to the query, expecting backtracking.

If button 'first' was choosen, then follow up by selecting either:
   'Next' - Retrieve the next answer to the query, or "no" if done.
   'Clear' - Clear the query if no more answer are required, and
              it wasn't exhausted using 'next'.

The output from the queries is displayed in the log window.  The output
is a Tcl list of the form:
   { Variable Name, Value, ... }

This can be used as is, or easily converted to a Tcl array where the variable
names act as indices into the array.  The first two elements are 'result' and
either 'true' or 'false'.

Note that the pets each log their own sound when queried, showing an
interaction from the logicbase back to the GUI.