Typol and Prolog

The current version of Typol is implemented in Prolog, and understanding how Prolog works will certainly make grasping Typol easier. Centaur uses Typol to define semantics rather than Prolog, however, for several reasons:

• Typol offers a general way of expressing semantic rules, independent of the target language, i.e., the language into which it is compiled (here, Prolog).
• Typol offers advanced interactive tracing mechanisms.
• Typol offers automatic type checking of instantiated variables, based on the language formalism definition.

Typol, like Prolog, manipulates abstract syntax tree fragments as terms, as in the expression:

plus(prod(integer 1, integer 2), integer 3)