Hi Adrian
You can use Data.Derive to do this for you:
http://www-users.cs.york.ac.uk/~ndm/derive/
Or DrIFT: http://repetae.net/~john/computer/haskell/DrIFT/
Thanks
Neil
On 7/7/07, Adrian Hey
Adrian Hey 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?
(Answering my own question) this seems to do the trick..
instance (Typeable1 map, 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 = typeOf1 m
Regards -- Adrian Hey
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