I'm learnined how to use GADTs, but for the moment I'm stuck on the following problem. some context first
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.