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: Keean. Graham Klyne wrote:
Hmmm, I'm not sure that I understand what you mean.
Considering my example (repeated below), is it that 'AtomicConcept' should be an algebraic datatype rather than just a type synonym? Or is there more?
Or... I just found John Hughes 1999 paper on Restricted Data Types in Haskell [1], which talks about representing class constraints by the type of its associated dictionary. Is this is what you mean?
#g --
[1] http://www.cs.chalmers.se/~rjmh/Papers/restricted-datatypes.ps
spike-overlap-ConceptExpr.lhs -----------------------------
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
Declare AtomicConcept and AtomicRole as instances of ConceptExpr and RoleExpr (AtomicRole is used by AL, and including AtomicConcept here for completeness).
instance ConceptExpr AtomicConcept where iConcept = undefined
...
To allow a common expression to support multiple description logics, we first define a wrapper class for DLConcept and DLRole:
class ConceptExpr c => ConceptWrapper cw c | cw -> c where wrapConcept :: c -> cw c -> cw c getConcept :: cw c -> c
Do this: data CW cw = CW cw class ConceptWrapper cw c | cw -> c 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:
This is line 30:
instance (ConceptWrapper cw c, ConceptExpr c) => ConceptExpr (cw c) where iConcept = iConcept . getConcept
instance ConceptWrapper (CW cw) c,ConceptExpr c) => ConceptExpr ((CW cw) c) where
Error message: Reading file "D:\Cvs\DEV\HaskellDL\spike-overlap-conceptexpr.lhs": ERROR "D:\Cvs\DEV\HaskellDL\spike-overlap-conceptexpr.lhs":30 - Overlapping inst ances for class "ConceptExpr" *** This instance : ConceptExpr (a b) *** Overlaps with : ConceptExpr AtomicConcept *** Common instance : ConceptExpr [Char]