Type signature "Maybe a" doesn't like "Just [Event]"
- by sisif
I'm still learning Haskell and need help with the type inference please!
Using packages SDL and Yampa
I get the following type signature from FRP.Yampa.reactimate:
(Bool -> IO (DTime, Maybe a))
and I want to use it for:
myInput :: Bool -> IO (DTime, Maybe [SDL.Event])
myInput isBlocking = do
event <- SDL.pollEvent
return (1, Just [event])
...
reactimate myInit myInput myOutput mySF
but it says
Couldn't match expected type `()'
against inferred type `[SDL.Event]'
Expected type: IO (DTime, Maybe ())
Inferred type: IO (DTime, Maybe [SDL.Event])
In the second argument of `reactimate', namely `input'
In the expression: reactimate initialize input output process
I thought Maybe a allows me to use anything, even a SDL.Event list?
Why is it expecting Maybe () when the type signature is actually Maybe a?
Why does it want an empty tuple, or a function taking no arguments, or what is () supposed to be?
