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module List
export length/1, reverse/1, empty/1, member/2, head/1, tail/1, filter/2,
foldl/3, foldr/3, map/2, flatten/1, drop/2, take/2, of/1, new/0
import Maybe exposing Maybe(..)
// Using the Erlang C BIF implementation.
//
foreign length :erlang :length :: |List(a)| -> Int
test length =
length([]) |> Assert.equal(_, 0)
length([1]) |> Assert.equal(_, 1)
length([1, 1]) |> Assert.equal(_, 2)
length([1, 1, 1]) |> Assert.equal(_, 3)
// Using the Erlang C BIF implementation.
//
foreign reverse :erlang :reverse :: |List(a)| -> List(a)
test reverse =
length([]) |> Assert.equal(_, [])
length([1, 2, 3, 4, 5]) |> Assert.equal(_, [5, 4, 3, 2, 1])
fn is_empty(list) =
list == []
test is_empty =
is_empty([]) |> Assert.true
is_empty([1]) |> Assert.false
fn member(list, elem) =
case list
| [] => False
| elem :: _ => True
| _ :: rest => member(rest, elem)
test is_member =
is_member([0, 4, 5, 1], 1) |> Assert.true
is_member([0, 4, 5, 7], 1) |> Assert.false
is_member([], 1) |> Assert.false
fn head(list) =
case list
| [] => Nothing
| elem :: _ => Just(elem)
test head =
head([0, 4, 5, 7]) |> Assert.equal(_, Just(0))
head([]) |> Assert.equal(_, Nothing)
fn tail(list) =
case list
| [] => Nothing
| _ :: rest => Just(rest)
test tail =
tail([0, 4, 5, 7]) |> Assert.equal(_, Just([4, 5, 7]))
tail([0]) |> Assert.equal(_, Just([]))
tail([]) |> Assert.equal(_, Nothing)
fn filter(list, fun) =
filter(list, fun, [])
test filter =
filter([], |x| True) |> Assert.equal(_, [])
filter([0, 4, 5, 7, 3], |x| True) |> Assert.equal(_, [0, 4, 5, 7, 3])
filter([0, 4, 5, 7, 3], |x| x > 4) |> Assert.equal(_, [5, 7])
filter([0, 4, 5, 7, 3], |x| x < 4) |> Assert.equal(_, [0, 3])
fn filter(list, fun, acc) =
case list
| [] => reverse(acc)
| x :: xs => (
new_acc = case fun(x)
| True => x :: acc
| False => acc
filter(xs, fun, new_acc)
)
fn map(list, fun) =
map(list, fun, [])
test map =
map([], |x| * 2) |> Assert.equal(_, [])
map([0, 4, 5, 7, 3], |x| x * 2) |> Assert.equal(_, [0, 8, 10, 14, 6])
fn map(list, fun, acc) =
case list
| [] => reverse(acc)
| x :: xs => map(xs, fun, fun(x) :: acc)
fn drop(list, n) =
case n <= 0
| True => list
| False => (
case list
| [] => []
| _ :: xs => drop(xs, n - 1)
)
test drop/2 =
drop([], 5) |> Assert.equal(_, [])
drop([1, 2, 3, 4, 5, 6, 7, 8], 5) |> Assert.equal(_, [6, 7, 8])
fn take(list, n) =
take(list, n, [])
fn take(list, n, acc) =
case n <= 0
| True => reverse(acc)
| False => (
case list
| [] => reverse(acc)
| x :: xs => take(xs, n - 1, x :: acc)
)
test take =
take([], 5) |> Assert.equal(_, [])
take([1, 2, 3, 4, 5, 6, 7, 8], 5) |> Assert.equal(_, [1, 2, 3, 4, 5])
fn of(x) =
[x]
test of() =
of([]) |> Assert.equal(_, [[]])
of(1) |> Assert.equal(_, [1])
fn new() =
[]
test new() =
new() |> Assert.equal(_, [])
fn flatten(lists) =
flatten(lists, [])
test flatten() =
flatten([]) |> Assert.equal(_, [])
flatten([[]]) |> Assert.equal(_, [])
flatten([[], [], []]) |> Assert.equal(_, [])
flatten([[1, 2], [], [3, 4]]) |> Assert.equal(_, [1, 2, 3, 4])
fn flatten(lists, acc) =
case lists
| [] => acc
| l :: rest => flatten(rest, acc ++ l)
fn foldl(list, acc, fun) =
case list
| [] => acc
| x :: rest => foldl(rest, fun(x, acc), fun)
test foldl() =
foldl([1, 2, 3], [], |x, acc| x :: acc)
|> Assert.equal(_, [3, 2, 1])
fn foldr(list, acc, fun) =
case list
| [] => acc
| x :: rest => fun(x, foldl(rest, acc, fun))
test foldr() =
foldr([1, 2, 3], [], |x, acc| x :: acc)
|> Assert.equal(_, [1, 2, 3])
|