Re: [Haskell-cafe] nooby question on typing

13 Sep 2008

      On Saturday September 13 2008, Han Joosten wrote:
...
...
 data Rule = RuRule
           | SgRule
           | GcRule
           | FrRule
               deriving (Eq,Show)
Here, Rule is a type constructor, whereas RuRule and others are data 
constructors. Just like:
...
data Bool = False | True
The type of RuRule is Rule and is not related to the RuRule type you are 
defining afterwards. What you want to do is probably this:
...
type Rules = [Rule]
 data Rule = Ru RuRule
           | Sg SgRule
           | Gc GcRule
           | Fr FrRule
             deriving (Eq,Show)
...
data RuRule
    = RuRule { rrsrt :: Char
             , rrant :: Expression
             , rrfps :: FilePos
             } deriving (Eq,Show)
...
data SgRule
    = SgRule { srfps :: FilePos
             , srsig :: Rule
             , srxpl :: String
             , srtyp :: (Concept,Concept)
             } deriving (Eq,Show)
...

You can now form a Rules list and use pattern matching on its members.

-- Gokhan

Re: [Haskell-cafe] nooby question on typing

Gökhan San