Finding & assembling class dictionaries from GHC plugins?

[Simon Peyton-Jones]

We just don't know how to start - ie how call the right functions from the type checker. Are there any resources explaining the relevant subset of the TcRnIf API?
And I for my part don't know where to start helping you!  Conal wrote

I don't think I need to construct dictionaries for new Typeable instances. I only need to find and assemble *existing* Typeable instances into combinations like Typeable [(Bool,Int -> String)], and I don't know how to do so in a GHC plug-in

That's exactly what the constraint solver does.  (TcSimplify and friends.)  But again I need more context.

I gather you are talking to Pedro too?  He knows a lot about this stuff.

Also there are a bunch of folk (Luite, Edsko) worked on the new front-end plugin stuff, and are much more expert in it than me.

We could have a skype call if that would help

S


From: Nicolas Frisby [mailto:nicolas.frisby at gmail.com]
Sent: 05 November 2013 14:36
To: Simon Peyton-Jones
Cc: ghc-devs at haskell.org; Conal Elliott
Subject: RE: Finding & assembling class dictionaries from GHC plugins?


On Nov 5, 2013 3:14 AM, "Simon Peyton-Jones" <simonpj at microsoft.com<mailto:simonpj at microsoft.com>> wrote:

>
> A core-level plug-in can't generate fresh instances.  There are some new plug-in hooks that fit earlier in the pipeline, which can.  Maybe you can use that, and generate a data type decl with "deriving Typeable"?

We're willing to do some awkward shoehorning in HERMIT to make this work in limited circumstances. (Hopefully including Conal's.)

We just don't know how to start - ie how call the right functions from the type checker. Are there any resources explaining the relevant subset of the TcRnIf API?

Thanks.

>
>
> From: ghc-devs [mailto:ghc-devs-bounces at haskell.org<mailto:ghc-devs-bounces at haskell.org>] On Behalf Of Conal Elliott
> Sent: 04 November 2013 20:08
> To: ghc-devs at haskell.org<mailto:ghc-devs at haskell.org>
> Subject: Finding & assembling class dictionaries from GHC plugins?
>
>
>
> I'm working on a GHC plugin (for compiling Haskell to hardware), and I need to synthesize Typeable (and maybe other) class dictionaries for a wide range of types, including composite types (functions, pairs, lists, etc). Can it be done, and how? I think I'm mainly looking for mechanics of finding existing class instances (however they're defined) and assembling them (for parametrized/composite dictionaries), rather than mechanisms specific to Typeable.
>
> Thanks, -- Conal
>
>
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