On 12/04/2011 06:53 AM, Scott Lawrence wrote:
[...] Some operators might take more than one list/stream as an argument, combining them in some way or another. Obviously, if the lists were different lengths, the operator would fail. I don't want that to happen at run time, so I want to check for it statically, presumably via the type system. I could do this manually:
type AList = [Event] type BList = [Event] type CList = [Event]
myMapish :: AList -> AList mySelect :: AList -> (Event -> Bool) -> BList myOtherSelect :: BList -> CList [...]
Just as a small side note, with the 'type' keyword, AList, BList, CList will /not/ be seen as separate types (but they're all the same type, namely [Event]). If you want separate types, you would use a newtype wrapper like newtype AList = AList [Event] deriving (some instances you want to derive from [Event]) -- Steffen