Type-safe fixity for builtins

[cimbul]

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)
	]