AST support : Add ADT, type alias, function/value to module declaration exposing node

[rundis]

Summary:

It would be nice to be able to add or remove a top level definition to/from what is exposed for a given module.

Details:

Given the following example: http://peg.arcanis.fr/3bbplj/4/

1. If a user positions the cursor somewhere within the range covered by the add function and selects to expose the function
2. add is added to the exposing clause (if not already present) for the module

Alternatively if add is already present and the user with the cursor in range of the add function selects to unexpose the function, it is removed from the exposing clause for the module

You would need at least the following:

• A way to identify that the user by cursor location is in an applicable top level def.
• A way to list what is already exposed
• A given node format to be able to add a new node to the exposing node of a module declaration
• Preferable a way to print the module declaration node in a elm-formatted manner, alternatively print the whole module, but then you also need to send current cursor position and get back new cursor position.
• For ADTs you would like to be able to do the same thing, but also for each type in the union type

Discussion

• If the module is already exposing everything (..) it should probably be a no-op (and/or a warning in the editor)