{-# OPTIONS_GHC -fglasgow-exts #-} module Test where import qualified Data.Set as S
Hi. I try to model the following: Hypotheses are build up from Rules, which itself are made of the type Rule. Because I may change the implementation later, I want to use type classes, which define the signature of my functions I will use in other modules.
class CRule r
class (CRule (CRulesRule r) ) => CRules r where type CRulesRule r
class (CRule (CHypoRule h), CRules (CHypoRules h) ) => CHypo h where type CHypoRules h type CHypoRule h hypo :: CHypoRules h -> CHypoRule h -> h
-- | Rule
data Rule = Rule Int deriving(Eq,Ord) instance CRule Rule
-- | Rules
type Rules = S.Set Rule instance CRules (S.Set Rule) where type CRulesRule (S.Set Rule) = Rule
-- | Hypothese
data Hypo = Hypo { open :: Rules , closed :: Rules }
instance CHypo Hypo where type CHypoRules Hypo = Rules type CHypoRule Hypo = Rule
hypo ro rc = Hypo { open=ro, closed=(S.singleton rc)}
So far so good. But why does now the last of the following lines not type check? It says: Couldn't match expected type `CHypoRules h' against inferred type `S.Set Rule' Couldn't match expected type `CHypoRule h' against inferred type `Rule'
rule1 = Rule 1 rule2 = Rule 2 rule3 = Rule 3 rules = S.fromList [rule1,rule2,rule3] ahypo = hypo rules rule1
Shouldn't be (CHypoRules Hypo) be associated with Rules and similar (CHypoRule) with Rule? Thanks a lot, Martin -- --------------------------------------------------------------- Dipl.-Wirtsch.Inf. (E.M.B.Sc.) Martin Hofmann Cognitive Systems Group Faculty Information Systems and Applied Computer Science University of Bamberg http://www.cogsys.wiai.uni-bamberg.de/members/hofmann http://www.inductive-programming.org