My guess is that you will eventually end up needing an
OverlappingInstances extension as well, and those two extensions
together can lead to some funny stuff. It *may* work, but I would
strongly recommend a newtype wrapper instead.
Michael
On Fri, Jan 28, 2011 at 8:28 AM, Max Cantor
I should have added, as long as the type-checker terminates and doesn't go into an infinite loop, is there any danger in doing this?
On Jan 28, 2011, at 2:24 PM, Max Cantor wrote:
With a bit of code, you can save a lot of effort if you add new types to Persistent:
instance Cereal.Serialize a => PersistField a where toPersistValue a = PersistByteString $ Cereal.encode a fromPersistValue (PersistByteString b) = Cereal.decode b fromPersistValue _ = Left "bad type for cereal encoded data" sqlType _ = SqlBlob isNullable _ = False
BUT, this requires UndecidableInstances. Is this a bad idea?
mc
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