michael rice
In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad?
Yes. Prelude> :m Control.Monad Prelude Control.Monad> let fn l = mzero `mplus` (return (head l)) `mplus` (return (last l)) Prelude Control.Monad> fn [1,3] :: Maybe Int Just 1 Prelude Control.Monad> fn [1,3] :: Maybe Float Just 1.0 Prelude Control.Monad> fn [1,2,3] :: [Int] [1,3] -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.