TODO

- call/1 has to be implemented properly. Current plan:
  - Implement in PIR, as normal predicate.
  - The input argument is then converted to a goal (this requires refactoring
    the compiler to move PAST-generation logic from Parrotlog::Compiler to
    Term).
  - Use PAST::Compiler to create POST, POST::Compiler to get PIR, and
    compreg('pir') to get the PIR compiled to bytecode (see Rakudo's
    src/cheats/eval.pm for how to embed it in a lexical scope).
  - Invoke the callable.
- Ideally, the compiler should flow differently.
  - Any file arguments are compiled as Prolog text
  - Any -e arguments, and anything input on the REPL is run as a query
    - Maybe it's possible to implement the REPL in Prolog, once enough of
      the scaffolding is in place?
  - Ultimately, this might be best done by adding a few more points where
    HLL::Compiler can be extended.