better type system based on py3 type hints

asmodehn commented 7 years ago

We should take inspiration from python3 type hints and https://www.python.org/dev/peps/pep-0483/

It would make things more solid, and would also provide simple python3 compatibility.

The type checker would operate at runtime, with the types providing a "contract" regarding the message structure and content.

Later we might want to extend it to provide contracts for complex node behaviors...

asmodehn commented 7 years ago

typing is supported for python 2.7 and mypy can be used for checking types (could be integrated with catkin_pip)

asmodehn commented 7 years ago

Note there is two distinct topics here :

improve our typechecker by matching types / structures / API from types hints PEP, hypothesis, etc.
add type hints to our implementation, so that, if people use mypy, they will detect type problems when using messages... but this is just a "nice to have" and not the core functionality. We still need to implement a dynamic type checking, so that we can extend it later to check for concurrency problems...

asmodehn commented 7 years ago

Another (complementary ?) option : https://andreacensi.github.io/contracts/

asmodehn commented 7 years ago

pycontracts seems to be lacking quite a few features, especially when comparing with hypothesis... We have currently implemented a very basic functional type checker, following hypothesis strategies, not sure if the effort in improving pycontracts is worth it.

Not sure what should be done here to improve/solidify this... maybe generating a type checker for python from a more rigorously typed language like idris ?

Anyway it seems to be quite distinct from defining messages for pyros : We want to give python a nice type system that can :

currently support py3 type hints
be extended later to support more dynamic contracts (like TLA+ : specifying a state machine for the type - we want to use it like contracts work in erlang, upon message reception to guarantee perceived state from another node )

This will help overall stability for our distributed system.

asmodehn commented 7 years ago

Python3 is now in progress in https://github.com/asmodehn/pyros-msgs/pull/14 However we are not doing anything with python3 types yet.

pyros-dev / pyros-msgs

better type system based on py3 type hints #3