[Haskell-cafe] Opaque types vs automated instance deriving

Alexey Karakulov ankarakulov at gmail.com
Tue Jun 21 00:07:34 CEST 2011

Hi all,
I encountered a problem when trying to

> derive makeBinary ''DiffTime

with help of *derive* package. The error was:

Not in scope: data constructor `MkDiffTime'

Which makes a sense, since it's not exported in Data.Time.Clock.
I bypassed the problem (yes, I'm too lazy to write instances by hands) with

> instance Binary UTCTime where
>  put =
>  get =

But it must be less efficient (and more verbose) than compile-time deriving.
If there was such a module like Data.Time.Clock.Internal, I could import it
to get hidden constructors (and maybe I'll have to fork the library for this

OTOH, is it possible to change the derive TH function so it can bypass
module encapsulation mechanism and access un-exported things?
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