Default.elm

Default.elm

module Default
    exposing
        ( Default
        , default
        , int
        , string
        , maybe
        , stubTask
        )

import Task exposing (Task)


{-| Phantom type to define default value of type `a`.
```
class Default a where
    default :: a
```
-}
type Default a
    = Default a


default : Default a -> a
default (Default a) =
    a


{-|
```
instance Default Int where
    default :: Int
    default = 0
```
-}
int : Default Int
int =
    Default 0


string : Default String
string =
    Default ""


maybe : Default a -> Default (Maybe a)
maybe (Default a) =
    Default <| Just a


{-| A Stub.
    stubTask int (Task.succeed 10)
    --> 0

    stubTask string (Task.succeed "foo")
    --> ""

    stubTask (maybe string) (Task.succeed <| Nothing)
    --> Just ""

    stubTask (maybe (maybe int)) (Task.succeed <| Just (Just 3))
    --> Just (Just 0)
-}
stubTask : Default a -> Task error a -> a
stubTask def _ =
    default def