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
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