At 16:16 23/11/04 +0000, Keean Schupke wrote:
The problem is that (cw c) overlaps with String. It will still ovarlap if you use data decl. it is the CW that needs to be a datatype. See Below:
Thanks. I've massaged that into something that compiles (copy below). I think I see why this works, but I still can't say that I find the revised structure entirely intuitive. I think the key feature is that wrapped instances of ConceptExpr are distinguished from "native" instances by the type constructor CW. That is, each instance type is distinguished by different known type constructor -- in this case, [] and CW. I need to noodle on the a while to see if the pattern fits my application, but I think I get the general idea. Of all the combinations I thought about making the type constructor part of the class method signatures was not one I'd tried. Also, I think declaring CW as a 'newtype' rather than 'data' captures the intent more directly. #g -- spike-overlap-ConceptExpr-datatyped.lhs --------------------------------------- Some given type and class declarations:
type AtomicConcepts a = [(AtomicConcept,[a] )] type AtomicRoles a = [(AtomicRole ,[(a,a)])]
type TInterpretation a = ([a],AtomicConcepts a,AtomicRoles a)
class (Eq c, Show c) => ConceptExpr c where iConcept :: Ord a => TInterpretation a -> c -> [a]
type AtomicConcept = String -- named atomic concept type AtomicRole = String -- named atomic role
Declare AtomicConcept as "base" instance of ConceptExpr.
instance ConceptExpr AtomicConcept where iConcept = undefined
To allow a common expression to support multiple description logics, define a wrapper type and class for DLConcept and DLRole:
newtype CW cw c = CW cw deriving (Eq,Show) class ConceptWrapper cw c | cw -> c where wrapConcept :: c -> (CW cw c) -> (CW cw c) getConcept :: (CW cw c) -> c
Using this, a ConceptWrapper can be defined to be an instance of ConceptExpr:
instance (Eq cw, Show cw, ConceptWrapper cw c,ConceptExpr c) => ConceptExpr (CW cw c) where iConcept i = iConcept i . getConcept
Now declare a pair containing a ConceptExpr to be an instance of ConceptWrapper:
type Wrap d c = (c,d)
instance ConceptWrapper (Wrap d c) c where wrapConcept c (CW (_,d)) = CW (c,d) getConcept (CW (c,_)) = c
------------ Graham Klyne For email: http://www.ninebynine.org/#Contact