cimbul/hasklog

A toy Prolog interpreter/compiler written in Haskell

hasklog's Issues

Flesh out interpreter tests

The tests for the Hasklog.Interpreter module currently only cover unification. Test the actual interpreter.

Set up continuous integration

Pick a CI service and configure:

• building
• testing
• linting
• coverage

Fix math rendering in manual

Github doesn't support math in ReStructuredText. Deploy the documentation to somewhere that does, or convert it to Markdown.

WAM-to-LLVM compiler

Add a simple WAM-to-LLVM compiler. Don't worry too much about optimization. Focus on something basic that works so we can iterate on it.

Helpful resources:

• http://www.stephendiehl.com/llvm/
• https://github.com/llvm-hs

Add source code formatter

Investigate Haskell formatters like Stylish, HIndent, and Brittany, and see if I can stand any of them.

Update manual to show Stack

I've been building this with Stack for a while. Update the old instructions in Manual.rst that reference Cabal.

Support wildcard patterns

Currently, _ is treated like any other atom, so if you write a pattern like foo(_, _), it will unify foo(A, A) or foo(B, B), but not foo(A, B). Treat this like a true wildcard pattern.

Fix orphaned instances

Enable the -Worphans GHC warning and reorganize the code to fix them.

Fix failing parser test

One of the parser tests has been failing for 8 years now. It's probably time to fix it.

  test/Hasklog/ParserSpec.hs:83:21: 
  1) Hasklog.Parser.term, with invalid input, fails to parse ":- a :- b"
       expected parse error
        but got: CompoundTerm ":-" [CompoundTerm ":-" [Atom "a",Atom "b"]]

Rename "functor" types/functions

"Functor" has different meanings in Prolog and Haskell. Data.functor and Complier.Functor make the code confusing and force us to hide Haskell's builtin Functor in imports. Rename them to something like "PFunctor" or maybe "Phunctor." 😄

Investigate switching to Megaparsec

End-to-end tests

Add some end-to-end tests, either written in Prolog itself or based on a transcript of interpreter sessions. Possibly something similar to this ISO conformance test suite, although since this implementation doesn't support I/O or second-order predicates, it will probably need some lifting on the Haskell side.

Improve REPL

Make the REPL more user-friendly with some of the features you usually find in a shell:

• history
• tab completion
• parenthesis matching

Have a closer look at SWI-Prolog and friends for some further ideas.

Possibilities:

• readline
• haskeline
• repline
• repl-toolkit

Add compiler tests

There aren't any tests for the Hasklog.Compiler module at the moment.

Type-safe fixity for builtins

The map of builtins uses an (identifier, fixity) pair as the key, but the builtin functions themselves all take a list of terms, and there is no static guarantee that we are passing the right number of terms. That forces us to define a lot of unnecessary fall-through cases. See if we can make this type-safe with a heterogenous map implementation or some kind of dependent type mechanism.

hasklog/src/Hasklog/Interpreter.hs

Lines 48 to 58 in aa7ff57

	-- | A map from a functor\/arity pair to a function that computes a builtin
	-- operation
	builtins :: (MonadIO m, Functor m) => Map (Identifier, Int) (Predicate m)
	builtins = M.fromList [
	(("fail", 0), bfail),
	(("true", 0), btrue),
	(("not", 1), bnot),
	(("consult", 1), bconsult),
	(("compile", 1), bcompile),
	(("op", 3), boperator)
	]

Collapse nested allocation state monads in compiler

The compiler module has a state monad within a state monad to keep track of the allocations of temporary and permanent variables. Consider collapsing this into a single state with a tuple of (temporary, permanent) allocations.

hasklog/src/Hasklog/Compiler.hs

Line 263 in aa7ff57

allocate :: VariableSet -> SimpleTerm -> StateT Allocation (State Allocation) TaggedTerm

Publish coverage report to Github Pages

Since hpc-coveralls is dead, it doesn't look like there's a good automated option for coverage reports. We could publish the HPC report to Github Pages instead.

WAM interpreter

Add a simple WAM interpreter so we can verify the compiler output makes sense.

Fix name shadowing

Enable the -Wname-shadowing GHC warning and fix the highlighted issues.

Clean up partial functions

I count about 12 undefineds in the code. See if we can avoid these with additional type safety.