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diff --git a/src/List.gleam b/src/List.gleam
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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])