Elm / Roc like language; pure, functional, statically typed, lazy

gistfile1.txt

import Http
import File
import Url

download : String -> Task () (HttpError Http.Error | FileError File.Error)
download = url ->
  content <- Http.getBytes url
  filename = Url.path url
    |> String.split "/"
    |> List.last
    |> Result.withDefault "data"
  File.write filename content

Tasks.txt

# Perform the list of tasks in parallel, returning a list of the resulting values.
# If any of the tasks fail, the entire sequence will fail.
Task.parallel : List (Task a err) -> Task (List a) err

# Perform the list of tasks sequentially, returning a list of the resulting values.
# If any of the tasks fail, the entire sequence will fail.
Task.sequential : List (Task a err) -> Task (List a) err

Task.join : Task a err1 -> Task b err2 -> Task (a, b) (err1 | err2)

Task.join3 : Task a err1 -> Task b err2 -> Task c err3 -> Task (a, b, c) (err1 | err2 | err3)

Task.andThen : (a -> Task b err2) -> Task a err1 -> Task b (err1 | err2)