I believe there is no such case. Data type contexts are a mis-feature and should never have been in Haskell.
Simon
| -----Original Message-----
| From: haskell-prime-bounces@haskell.org [mailto:haskell-prime-
| bounces@haskell.org] On Behalf Of Thomas Schilling
| Sent: 19 July 2010 23:14
| To: haskell-prime@haskell.org
| Subject: Re: Propsal: NoDatatypeContexts
|
| On 18 July 2010 22:59, Ian Lynagh wrote:
| > I have made a proposal to remove support for that context (ticket #139).
| > More details are on the proposal wiki page:
| >
| > http://hackage.haskell.org/trac/haskell-prime/wiki/NoDatatypeContexts
|
| +1
|
| I would be interested in a case where it actually *is* a good idea to
| use such contexts. From my understanding, if you want to enforce the
| constraints on users of your library you can still export it as an
| abstract data type and put the constraints on the functions that use
| it.
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