Hi Simon,

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. Pointers greatly appreciated!

-- Conal


On Tue, Nov 5, 2013 at 1:13 AM, Simon Peyton-Jones <simonpj@microsoft.com> wrote:

I’m not sure what you mean by “synthesise”.

 

Typeable instances can no longer be hand-written; they must be derived by GHC.  That’s to keep them type-secure.

 

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”?


Simon

 

From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Conal Elliott
Sent: 04 November 2013 20:08
To: ghc-devs@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