9 Jul
2008
9 Jul
'08
11:01 p.m.
On Wed, Jul 9, 2008 at 9:40 PM, Ron Alford
Ok, but to make it part of a record, it needs to implement Data: data Expr f = In (f (Expr f)) deriving Data
but this gives No instances for (Data (f (Expr f)), Typeable (Expr f)) arising from the 'deriving' clause of a data type declaration at Planning/Wouter.hs:77:0-42
The Data class has a requirement that any instances are also instances of Typeable, so you'd really want
data ... = ... deriving (Data, Typeable)
Except that I couldn't derive Typeable for your particular data type. It isn't immediately obvious to me that the "Typeable" family of classes deal at all with higher-kinded type constructors, but I didn't look that hard. -Antoine