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
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