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module Maybe
export Maybe(..), is_just/1, is_nothing/1, map/2, flatten/1, flat_map/2,
unwrap/2
type Maybe(x)
= Just(x)
| Nothing
fn is_just(maybe) =
case maybe
| Just(_) => True
| Nothing => False
test is_just() =
is_just(Just(1)) |> Assert.true
is_just(Nothing) |> Assert.false
fn is_nothing(maybe) =
case maybe
| Just(_) => False
| Nothing => True
test is_nothing() =
is_nothing(Just(1)) |> Assert.false
is_nothing(Nothing) |> Assert.true
fn map(maybe, fun) =
case maybe
| Just(x) => fun(x)
| Nothing => Nothing
test map() =
map(Just(1), |x| x + 1) |> Assert.equal(_, Just(2))
map(Nothing, |x| x + 1) |> Assert.equal(Nothing)
fn flatten(maybe) =
maybe
|> unwrap(_, Nothing)
test flatten() =
flatten(Just(Just(1))) |> Assert.equal(Just(1))
flatten(Just(Nothing)) |> Assert.equal(Nothing)
flatten(Nothing) |> Assert.equal(Nothing)
fn flat_map(maybe, fun) =
maybe
|> map(_, fun)
|> flatten
test flat_map() =
flat_map(Nothing, |x| Just(x + 1)) |> Assert.equal(Nothing)
flat_map(Just(1), |x| Just(x + 1)) |> Assert.equal(Just(2))
flat_map(Just(1), |_| Nothing) |> Assert.equal(Nothing)
fn unwrap(maybe, fallback) =
case maybe
| Just(v) => v
| Nothing => fallback
test unwrap() =
unwrap(Just(1), 50) |> Assert.equal(1)
unwrap(Nothing, 50) |> Assert.equal(50)
|