[Haskell-cafe] Trying to make a Typeable instance
ndmitchell at gmail.com
Sat Jul 7 06:41:11 EDT 2007
> data ListGT map k a
> = Empt
> | BraF ![k] a !(map (ListGT map k a))
> | BraE ![k] !(map (ListGT map k a))
> deriving( Typeable )
Not in Haskell, only in GHC.
> On 7/7/07, Adrian Hey <ahey at iee.org> wrote:
> > Hello,
> > I'm trying to make the type (ListGT map k a) an instance of Typeable,
> > where map is kind (* -> *).
> > data ListGT map k a
> > = Empt
> > | BraF ![k] a !(map (ListGT map k a))
> > | BraE ![k] !(map (ListGT map k a))
> > I thought I'd cracked it with something like this..
> > instance (Typeable (map (ListGT map k a)), Typeable k, Typeable a) =>
> > Typeable (ListGT map k a) where
> > typeOf lgt = mkTyConApp (mkTyCon " Data.Trie.General.ListGT")
> > [mTypeRep, kTypeRep, aTypeRep]
> > where BraF [k] a m = lgt -- This is just to get types for k a m !!
> > kTypeRep = typeOf k
> > aTypeRep = typeOf a
> > mTypeRep = typeOf m
> > However, showing the resulting TypRep gives a stack overflow. I wasn't
> > too surprised about this, so I tried replacing the last line with..
> > mTypeRep = mkTyConApp (typeRepTyCon (typeOf m)) 
> > ..thinking that this would make it terminate. But it doesn't.
> > Could someone explain how to do this?
> > Thanks
> > --
> > Adrian Hey
> > _______________________________________________
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> > Haskell-Cafe at haskell.org
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