[Haskell-cafe] Determine instance method from class method callsite

[Robin Palotai]

My conclusion so far: there's no royal way. One can get the instance
dictionary DFunId pretty easy, but then access to the Typechecked AST of
the instance declaration is really needed to find all the method bindings
$c... (that get applied when constructing the dictionary $d...).

2017-09-19 7:38 GMT+02:00 Robin Palotai <palotai.robin at gmail.com>:

> Sorry, I messed up subject and mailing list. Copying to both list now
> after the mistake (wanted only ghc-devs for specificity).
>
> Thanks!
>
> 2017-09-19 7:36 GMT+02:00 Robin Palotai <palotai.robin at gmail.com>:
>
>> Hello GHC devs,
>>
>> Before inventing the wheel, want to check if there is a GHC API way to
>> look up the (fully) resolved instance method from a class method.
>>
>> For example, given a code
>>
>>     data Foo Int deriving Show
>>
>>     bar = show (Foo 3)
>>
>> when inspecting the Typechecked AST for bar's show call, I would like to
>> get to the Name / Id of 'show' of the 'Show' typeclass.
>>
>> I believe I could use splitHsSigmaTy on the HsType of the function call
>> to get the context, and then evaluate the HsWrapper somehow to find out
>> what instance dictionary is applied to the class restriction in the
>> context, and then look up the instance method from the dictionary..
>>
>> Two questions:
>>
>> 1) Is there maybe functionality for this?
>>
>> 2) If not, is there any guarantee about the constraint order in the
>> context, at the method call? So I could more easily determine which
>> constraint's application to look for..
>>
>> Any hints welcome && Thank you!
>> Robin
>>
>
>
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