Question

I have the following sample code

let x = [return 1::IO(Int), return 2::IO(Int)]

So x is a list of IO(Int)s.
maximum is a function which returns the maximum of a list, if the things in the list are Ords.
How do I “map” maximum to run on this list of IO(Int)s?

Answer 1

First sequence the array into IO [Int] and then run maximum on it using liftM:

liftM maximum (sequence yourList) :: IO Int