| The following doesn't seem to work. Is this a limitation of the current
| implementation or will it never work? Are there any work arounds without
| introducing extra type params into the data type E?
|
| > class G a b | a -> b where
| > data E a :: *
| > wrap :: b -> E a
| > unwrap :: E a -> b
|
| > instance G a b where
| > data E a = EC b -- this line - the b is not in scope.
| > wrap = EC
| > unwrap (EC b) = b
|
| I get "Not in scope: type variable `b'".
That's a bug. b should be in scope
However, your program is very suspicious! Associated data types *replace*
functional dependencies, so you should not use both. Your probably want
something like
class G a where
data E a :: *
wrap :: a -> E a
unwrap :: E a -> a
Simon
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