Standard library `map` function for Either and Optional

Questions
1

Is there a function in the standard library that allows me to map over Optionals or Eithers?

I didn’t find it in the documentation and the following snippet also doesn’t compile:

testEMap : Script ()
testEMap = script do
  let x : Either Int Int = Right 42
  let x2 = map (\val -> show x <> "hello") x 
  pure ()

It fails with couldn't match expected type ‘[a0]’ with actual type ‘Either Int Int’

(I know how I could write a map function myself, I am just surprised I can’t find one.)

2

Option and Either are both instances of Functor so you can use fmap:

testEMap : Script ()
testEMap = script do
  let x : Either Int Int = Right 42
  let x2 = fmap (\val -> show x <> "hello") x 
  pure ()
1 Like
3

Thanks!

4

@Arne_Gebert

L33t D@ml hackers use <$> and point free style to avoid @cocreature 's bug!

let x2 =  (<> "hello") . show <$> x