Better transformer API

[tilk]

This PR utilizes def_helper mechanisms to create a nicer API for using transformers. Following changes in interpreting the function arguments of the transformer classes are made:

• The module parameter is now optional.
• Instead of taking a record of method inputs (arg) the functions can take individual record fields, just like methods defined via def_method.

Also, specializations of def_helper were moved closer to their use sites, so that the dependencies on types would resolve correctly. If someone has a better idea, I'd like to hear it.

To do:

• Update docstrings.

[lekcyjna123]

I have mixed feelings. I like the simplicity of interface and the reduction of boilerplate. But we are loosing consistency. Earlier everywhere first argument had to be TModule. Now in transformer API it wouldn't be needed, but e.g. in method calls it will be still required. Nevertheless I am ready to approve such changes.

[lekcyjna123]

Shouldn't be func annotated as CallableOptParam? I have the same question regarding mock_def_helper and method_def_helper.

[tilk]

It could, but it basically changes nothing because of the ... parameter specification.

[tilk]

But we are loosing consistency.

I think we are actually gaining consistency, as:

• Keyword arguments allows to define functions just like method definitions.
• The filter function can now be defined consistently with your validate_arguments feature. The validating function cannot get a TModule argument, because it's called outside of the transactional circuit (in the transaction scheduler).

Also:

• The TModule argument was basically a hack to allow the use of methods as functions. I expect this argument will not be needed in most use cases.
• The presence or lack of the TModule argument actually signals something meaningful: it says that the function can do method calls in the context of the transformer. (There is unfortunately no way to guarantee "purity", as a function might use an external TModule to do some stuff. I sure hope this use will be avoided though.)