hspl

Abstract

hspl is a very simple interpreter of a subset of Prolog written in Literate Haskell. I wrote it as an exercise to grasp basics of both Prolog and Haskell.

It may be interesting to you if you want to play around with either Prolog or Haskell, or if you're interested in some of topics below.

Feel free to contact me if you have any questions.

Topics

• "Nondeterministic" monadic parsers
• Global state in Haskell using Control.Monad.State
• Basic implementation of Prolog resolution method and backtracking

Unsupported Features

• Most of Prolog's features: arithmetics, operators (such as =, is, etc.)
• I didn't use monad transformers to intermix State with IO, so I cannot use ie. the consult("filename") predicate to load the file during execution

Docs

I didn't provide any "User's Manual", as there are hardly any users to this; it's meant as a learning aid to other novice Haskell programers.

Tests

Sure enough, there are bugs.

Test inputs may be found in tests/. I didn't provide an automated test runner, but generally whatever you find in tests/ should work well.

In the unlikely case that you needed basic rules for list manipulation, for example, you may find them in tests/lists.pl.

Overview

The sources constitute of:

• Main.hs, the application's entry point
• Interpreter.lhs, the Prolog interpreter itself, and
• Parser.lhs, the monadic parser of Prolog.

Sources

• My question on Code Review Stack Exchange regarding the Parser module.