On 09.02.2011 20:57, Chris Smith wrote:
On Wed, 2011-02-09 at 18:15 +0100, Cristiano Paris wrote:
I've a type problem that I cannot solve and, before I keep banging my
head against an unbreakable wall, I'd like to discuss it with the
list.
If I'm understanding your high-level goals correctly, then you're going
about things the wrong way. It looks like in your "Sealed" type, you're
accumulating a list of type class constraints that are needed by a
phantom type, in order to access the value. But type classes are open;
anyone can make any new type an instance of the type class whenever they
want.
It's possible to have closed type classes. Trick consist in adding
unsatisfiable constraint. For example:
> -- This type class is not exported
> class Private a
> class Private a => PRead a
If Private is not exported one cannot add instances to PRead.
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