Hello, I'm beginner too but i will try to respond. I would do this like that:
type Cost = Int type ID = Int type Student = String type Activity = String
data Table k v = PopTable { tableName :: String , tableList :: [(k, v)] } deriving (Show, Read)
type Students = Table ID Student type ActivityCosts = Table Activity Cost type StudentActivities = Table Activity ID
loaders :: [ProgramName] loaders = [CStudents $ PopTable "students" loadStudentIDs, CActivityCosts $ PopTable "costs" loadActivityCosts]
data ProgramName = CStudents Students | CActivityCosts ActivityCosts | CStudentActivities StudentActivities
loadStudentIDs :: [(ID, Student)] loadStudentIDs = [(1, "marcel"), (2, "alphonse")]
loadActivityCosts :: [(Activity, Cost)] loadActivityCosts = [("work", 10)]
There is no need for a GATD. All you need here, is to hide your different types into one named ProgramName. Once this is done, you can have a list of ProgramName. In the ProgramName datatype, you see different contructors, which allow you to contruct a ProgramName. In GHCI:
:t CStudents CStudents :: Students -> ProgramName
Cheers,
Corentin
Michael Litchard
newtype Cost = Cost Int newtype ID = ID Int newtype Student = Student String newtype Activity = Activity String data Table k v = PopTable { tableName :: String , tableList :: [(k, v)] } deriving (Show, Read) type Students = Table ID Student type ActivityCosts = Table Activity Cost type StudentActivities = Table Activity ID
I want to do something like this
loaders = [("students", loadStudentIDs), ("costs", loadActivityCosts), ("activities", loadStudentActivities)]
But I can't have list with multiple types. Okay so ski (from #haskell) suggested I use a GADT. This is new territory for me. Here's what it looks like right now. data ProgramName :: * -> * where PNStudents :: ProgramName Students PNCosts :: ProgramName ActivityCosts PNActivities :: ProgramName StudentActivities Now I should be able to use this to define a data structure called "loaders" that contains three tuples ("students", loadStudentIDs), ("costs", loadActivityCosts), and ("activities", loadStudentActivities). So, what would "loaders" look like? I've done some reading but it's not sunk in yet. _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners