Adds split to list stdlib

5 files changed, 64 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 02cb49d..8f6b5e3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,7 @@
 - The `map_dict` module gains `update`, `merge` and `delete` functions.
 - The `bool` module gains a `compare` function.
 - The `int` module gains a `compare` function.
-- The `list` module gains `range`, `repeat`, and `strict_zip` functions.
+- The `list` module gains `range`, `repeat`, `split`, and `strict_zip` functions.
 
 ## v0.1.2 - 2019-04-25
 
diff --git a/gen/src/list.erl b/gen/src/list.erl
index 96dd7d2..1395112 100644
--- a/gen/src/list.erl
+++ b/gen/src/list.erl
@@ -1,7 +1,7 @@
 -module(list).
 -compile(no_auto_import).
 
--export([length/1, reverse/1, is_empty/1, contains/2, head/1, tail/1, filter/2, map/2, index_map/2, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, fold/3, fold_right/3, find/2, all/2, any/2, zip/2, strict_zip/2, intersperse/2, at/2, unique/1, sort/1, range/2, repeat/2]).
+-export([length/1, reverse/1, is_empty/1, contains/2, head/1, tail/1, filter/2, map/2, index_map/2, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, fold/3, fold_right/3, find/2, all/2, any/2, zip/2, strict_zip/2, intersperse/2, at/2, unique/1, sort/1, range/2, repeat/2, split/2]).
 
 length(A) ->
     erlang:length(A).
@@ -331,3 +331,21 @@ do_repeat(A, Times, Acc) ->
 
 repeat(A, Times) ->
     do_repeat(A, Times, []).
+
+do_split(List, N, Taken) ->
+    case N =< 0 of
+        true ->
+            {reverse(Taken), List};
+
+        false ->
+            case List of
+                [] ->
+                    {reverse(Taken), []};
+
+                [X | Xs] ->
+                    do_split(Xs, N - 1, [X | Taken])
+            end
+    end.
+
+split(List, N) ->
+    do_split(List, N, []).
diff --git a/gen/test/list_test.erl b/gen/test/list_test.erl
index b00d507..705cb3c 100644
--- a/gen/test/list_test.erl
+++ b/gen/test/list_test.erl
@@ -1,7 +1,7 @@
 -module(list_test).
 -compile(no_auto_import).
 
--export([length_test/0, reverse_test/0, is_empty_test/0, contains_test/0, head_test/0, tail_test/0, filter_test/0, map_test/0, traverse_test/0, drop_test/0, take_test/0, new_test/0, append_test/0, flatten_test/0, fold_test/0, fold_right_test/0, find_test/0, all_test/0, any_test/0, zip_test/0, strict_zip_test/0, intersperse_test/0, at_test/0, unique_test/0, sort_test/0, index_map_test/0, range_test/0, repeat_test/0]).
+-export([length_test/0, reverse_test/0, is_empty_test/0, contains_test/0, head_test/0, tail_test/0, filter_test/0, map_test/0, traverse_test/0, drop_test/0, take_test/0, new_test/0, append_test/0, flatten_test/0, fold_test/0, fold_right_test/0, find_test/0, all_test/0, any_test/0, zip_test/0, strict_zip_test/0, intersperse_test/0, at_test/0, unique_test/0, sort_test/0, index_map_test/0, range_test/0, repeat_test/0, split_test/0]).
 
 length_test() ->
     expect:equal(list:length([]), 0),
@@ -162,3 +162,11 @@ repeat_test() ->
     expect:equal(list:repeat(2, 3), [2, 2, 2]),
     expect:equal(list:repeat(<<"x">>, 5),
                  [<<"x">>, <<"x">>, <<"x">>, <<"x">>, <<"x">>]).
+
+split_test() ->
+    expect:equal(list:split([], 0), {[], []}),
+    expect:equal(list:split([0, 1, 2, 3, 4], 0), {[], [0, 1, 2, 3, 4]}),
+    expect:equal(list:split([0, 1, 2, 3, 4], -2), {[], [0, 1, 2, 3, 4]}),
+    expect:equal(list:split([0, 1, 2, 3, 4], 1), {[0], [1, 2, 3, 4]}),
+    expect:equal(list:split([0, 1, 2, 3, 4], 3), {[0, 1, 2], [3, 4]}),
+    expect:equal(list:split([0, 1, 2, 3, 4], 9), {[0, 1, 2, 3, 4], []}).
diff --git a/src/list.gleam b/src/list.gleam
index 352fc77..40c097e 100644
--- a/src/list.gleam
+++ b/src/list.gleam
@@ -274,3 +274,18 @@ fn do_repeat(a, times, acc) {
 pub fn repeat(a, times) {
   do_repeat(a, times, [])
 }
+
+fn do_split(list, n, taken) {
+  case n <= 0 {
+  | True -> {reverse(taken), list}
+  | False ->
+      case list {
+      | [] -> {reverse(taken), []}
+      | [x | xs] -> do_split(xs, n - 1, [x | taken])
+      }
+  }
+}
+
+pub fn split(list, n) {
+  do_split(list, n, [])
+}
diff --git a/test/list_test.gleam b/test/list_test.gleam
index fb32387..2311365 100644
--- a/test/list_test.gleam
+++ b/test/list_test.gleam
@@ -312,3 +312,23 @@ pub fn repeat_test() {
   list:repeat("x", 5)
   |> expect:equal(_, ["x", "x", "x", "x", "x"])
 }
+
+pub fn split_test() {
+  list:split([], 0)
+  |> expect:equal(_, {[], []})
+
+  list:split([0, 1, 2, 3, 4], 0)
+  |> expect:equal(_, {[], [0, 1, 2, 3, 4]})
+
+  list:split([0, 1, 2, 3, 4], -2)
+  |> expect:equal(_, {[], [0, 1, 2, 3, 4]})
+
+  list:split([0, 1, 2, 3, 4], 1)
+  |> expect:equal(_, {[0], [1, 2, 3, 4]})
+
+  list:split([0, 1, 2, 3, 4], 3)
+  |> expect:equal(_, {[0, 1, 2], [3, 4]})
+
+  list:split([0, 1, 2, 3, 4], 9)
+  |> expect:equal(_, {[0, 1, 2, 3, 4], []})
+}