how to return the literal 1 as Maybe Integer?

I am learning Haskell and having trouble returning literal 1 as Maybe Integer

alwaysOne:: Integer -> Maybe Integer
alwaysOne n = 1

raises

error:
    • No instance for (Num (Maybe Integer))
        arising from the literal ‘1’
    • In the expression: 1
      In an equation for ‘alwaysOne’: alwaysOne n = 1
   |
14 | alwaysOne n = 1
   |             ^

>Solution :

having trouble returning literal 1 as Maybe Integer

The Maybe a type has two data constructors:

data Maybe a = Nothing | Just a

You need to use one of these data constructors if you want to produce a Maybe Integer value. What you want is to pass the 1 to the Just data constructor:

alwaysOne:: Integer -> Maybe Integer
alwaysOne n = Just 1

That is, Just takes a value of any type and produces a value of Maybe parametrized for that type:

Just :: a -> Maybe a

a above is inferred as Integer in your case.

Analogously, if you wanted to define alwaysNothing:

alwaysNothing :: Integer -> Maybe Integer
alwaysNothing _ = Nothing