Errors:
- Not supported
- Only * is supported
- Expected * in *, but got *
- Divergent type in (construct), (location 1), (location 2)
- Unknown field
- Unbounded variable
- Different variable
- Different domain
- * is not subclass of *
- Type not equal
- Incorrect number of parameters

Symbol Resolution:
- Find class references, load them all in TopLevelContext.
- Find unbounded identifiers/functions in functions.
- `inspect.getmodule(x)` every unknown `x` if not primitive/list of primitives,
  check their files recursively by getting their file path, cache with
  (normalized) path as key.

TopLevelContext/InferenceContext:
- Restrict visibility by user defined function.