Type/type class information in GHC plugin

[Richard Eisenberg]

Hello Shen,

I’m not sure if I’m answering exactly what you’re asking, but perhaps this can move you in the right direction:

- To apply an expression to some types, you can use mkTyApps, in the CoreSyn module. The type of that function (Expr b -> [Type] -> Expr b) should be self-explanatory.

- To get the instance environments (where all class instances are stored), use tcGetInstEnvs, in the Inst module.

- Then, to get the actual dictionary, you can do the lookup with lookupInstEnv, in the InstEnv module.

Does this move you in the right direction?

Richard

On Apr 24, 2014, at 5:37 PM, Shen Chen Xu <shenchenxu at gmail.com> wrote:

> Hello everyone,
> 
> I would like to write a GHC plugin which adds wrapper to functions. Say I have
> a function
> 
> addWrapper :: Ord a => (a -> b) -> a -> b
> 
> which is supposed to transform (assuming the argument is in the Ord class)
> 
> foo = \ x -> ...
> 
> into
> 
> foo = addWrapper (\ x -> ...)
> 
> This works fine if I'm only interested in wrapping functions of type Int ->
> Int, in which case I make addWrapper to also have type
> 
> addWrapper :: (Int -> Int) -> Int -> Int
> 
> and use mkCoreApp to apply addWrapper to the right hand side.
> 
> However, if I want it to be polymorphic as described above, the transformed GHC
> Core for an Int -> Int function should look like
> 
> foo = addHook @ GHC.Types.Int @ GHC.Types.Int GHC.Classes.$fOrdInt (\ x -> ...)
> 
> My question is, given the right hand side of foo, how do I construct the
> type/type class information inside Core shown above?
> 
> Cheers,
> Shen
> 
> 
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