I think similar things have been asked before, but I couldn't find anything
specific.
I have a data type with attributes. These attributes have different types.
Right now I'm using a lot of boilerplate like that:
> data Gender = Masc | Fem | Neutr
> ...
> data Attr = Gender Gender | Cat Cat | Graph Graph | ...
> data Type = TypeCat | TypeGender | ... deriving Eq
>
> myTypeOf (Gender _) = TypeGender
> myTypeOf (Cat _) = TypeCat
> ...
> myTypeOf _ = TypeError
>
> data Segment = Seg { attrs :: [Attr] }
>
> attr f seg = seg { attrs = f (attrs seg) }
>
> gattr :: Type -> [Attr] -> Maybe Attr
> gattr theType [] = fail "attribute not found"
> gattr theType (a:as) = if myTypeOf a == theType then return a else gattr
theType as
>
> cat :: Cat -> Segment -> Segment
> cat c = attr ((Cat c):) -- set value
>
> gcat :: Segment -> Maybe Cat -- get value
> gcat = deCat . gattr TypeCat . attrs
> where deCat (Just (Cat c)) = c
> deCat x = x
> ...
Does anyone have some suggestions for making this more concise?
Generic Haskell? Tricky type classes?
Thanks,
Markus
--
Markus Schnell
Infineon Technologies AG, CPR ET
Tel +49 (89) 234-20875
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