I am trying to solve a problem from "The Craft of Functional Programming" book: 14.38 ... define the function: data Maybe a = Nothing | Just a composeMaybe :: (a -> Maybe b) -> (b -> Maybe c) -> (a -> Maybe c) using functions: squashMaybe :: Maybe (Maybe a) -> Maybe a squashMaybe (Just (Just x)) = Just x squashMaybe _ = Nothing mapMaybe :: (a -> b) -> Maybe a -> Maybe b mapMaybe f Nothing = Nothing mapMaybe f (Just x) = Just (f x) As a first step to the solution I defined auxilary function: f1 f g x = mapMaybe f (g x) GHCi gives the following type for this function: f1 :: (a -> b) -> (t -> Maybe a) -> t -> Maybe b ^^^ Q: I don't quite understand this signature. I would expect this instead (by mapMaybe definition): f1 :: (a -> b) -> (t -> Maybe a) -> Maybe b
From where does the second 't' come from? What are the arguments and what f1 returns in this case?