Yes, sorry, a part of my talk at Elixirconf was about using the AST as the 
source for "intelligent" refactoring tools; renaming functions, inlining 
variables, extracting functions, etc.
It should be online soon, I think, slides are here 
<https://docs.google.com/presentation/d/15_xKuL_H4Eu-EkGarxVixCk192858avE1ef1gmcVKoc/edit?usp=sharing>
. 

Arjan

On Tuesday, April 23, 2019 at 6:29:20 PM UTC+2, Steve Morin wrote:
>
> Arjan Scherpenisse 
> What is you're use-case?
>
> On Tue, Apr 23, 2019 at 4:20 AM Arjan Scherpenisse <[email protected] 
> <javascript:>> wrote:
>
>> I actually discussed a solution like this with José in Prague but this 
>> will also become complicated very quickly, especially as these primivite 
>> nodes can be nested (e.g. keyword lists and normal lists). Maintaining the 
>> correct position in the parent is also problematic when you want to do 
>> something with the child nodes, for instance if you write an AST transform 
>> to swap 2 parameters of a function call, the comments would not get swapped.
>>
>> For the short term I've put this subject to rest. My opinion is that for 
>> tooling that depends on code -> ast -> code transforms, we need more 
>> specialized tooling. For instance, we cannot assume that the input source 
>> code is already properly formatted; Ideally a source code modification tool 
>> should work with all kinds of source code, and a transformation should only 
>> affect the local scope, and not, for instance, reformat all of the output. 
>> I could even imagine it working with code that is not syntactically 
>> correct. That is a subject that the Elixir parser was just not meant to do, 
>> and trying to squeeze comments into the AST would not solve this.
>>
>> I have been looking at the Wrangler 
>> <https://github.com/RefactoringTools/Wrangler/> source code, which is a 
>> set of Erlang refactoring tools, but I have not come very far yet. It is an 
>> interesting source of information though. 
>>
>> Arjan
>>
>> On Tuesday, April 23, 2019 at 12:18:07 PM UTC+2, [email protected] wrote:
>>>
>>> What about "hoisting" the comments into the metadata of the surrounding 
>>> block for the primitive AST nodes? 
>>> This means that we need to be able to specify *where* in a `:__block__` 
>>> a comment ought to occur, which shouldn't be a problem: The only cases 
>>> where this information will be out of date is when macro rewriting alters 
>>> the AST, which is a situation that would probably remove the comments 
>>> anyway.
>>> (so e.g. a formatter would need to move comments with the code just as 
>>> is the case currently, but optimization tools would not care about comments 
>>> anyway).
>>>
>>> This 'where' might take the format of a keyword-list, with 
>>> half-line-numbers as keys and strings (containing the actual comments) as 
>>> values. 'half-line-numbers ' go from 0 up to and including 
>>> `2*n_lines_in_block`. Even numbers are comments occuring before (e.g. on 
>>> the line above) `div(half-line-number, 2)`. Odd numbers are comments 
>>> occuring after (at the end of the same line as) `div(half-line-number/2)`.
>>>
>>>
>>> So 
>>>
>>> quote do
>>>   # one is the lonliest number
>>>   1
>>>   2 # two is the smallest prime
>>>   3
>>>   # I am at the end
>>> end
>>>
>>>
>>>
>>> would compile to 
>>> {:__block__, [comments: [0 => "one is the lonliest number", 3 => 
>>> "two is the smallest prime", 6 => "I am at the end"]], [1,2,3]}
>>>
>>>
>>> ~Marten / Qqwy
>>>
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>
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> Steve Morin | Hacker, Entrepreneur, Startup Advisor 
> twitter.com/SteveMorin | stevemorin.com
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