Is there a reason why automatic derivation of Ord without Eq doesn't do "the sensible thing" and just derive Eq anyway?
newtype Id a = Id { a :: String } deriving (Read, Show, Eq, Ord) newtype Ego a = Ego { b :: String } deriving (Read, Show, Ord)
Both will type check, but if you try any (in)equality operators on the second they'll be spat back at you.
*Main> let e1 = Ego "" *Main> let e2 = Ego "" *Main> e1 < e2
<interactive>:1:0: No instance for (Eq (Ego a)) arising from use of `<' at <interactive>:1:0-6 Possible fix: add an instance declaration for (Eq (Ego a)) In the expression: e1 < e2 In the definition of `it': it = e1 < e2
It doesn't seem *much* of a hardship, but it wasn't what I expected. I'm not used to GHC accepting input and silently dropping stuff it doesn't like... Cheers, D.