Add list:zip

4 files changed, 46 insertions, 3 deletions

diff --git a/gen/src/list.erl b/gen/src/list.erl
index 97c0579..39a30a3 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, traverse/2, drop/2, take/2, new/0, append/2, flatten/1, fold/3, fold_right/3, find/2, all/2, any/2]).
+-export([length/1, reverse/1, is_empty/1, contains/2, head/1, tail/1, filter/2, 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]).
 
 length(A) ->
     erlang:length(A).
@@ -201,3 +201,15 @@ any(List, F) ->
                     true
             end
     end.
+
+zip(L1, L2) ->
+    case {L1, L2} of
+        {[], _} ->
+            [];
+
+        {_, []} ->
+            [];
+
+        {[X1 | Rest1], [X2 | Rest2]} ->
+            [{X1, X2} | zip(Rest1, Rest2)]
+    end.
diff --git a/gen/test/list_test.erl b/gen/test/list_test.erl
index df9acac..9cb1ac3 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]).
+-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]).
 
 length_test() ->
     expect:equal(list:length([]), 0),
@@ -103,3 +103,10 @@ any_test() ->
     expect:equal(list:any([1, 2, 3, 4, 5], fun(X) -> X =:= 2 end), true),
     expect:equal(list:any([1, 2, 3, 4, 5], fun(X) -> X < 0 end), false),
     expect:equal(list:any([], fun(_) -> false end), false).
+
+zip_test() ->
+    expect:equal(list:zip([], [1, 2, 3]), []),
+    expect:equal(list:zip([1, 2], []), []),
+    expect:equal(list:zip([1, 2, 3], [4, 5, 6]), [{1, 4}, {2, 5}, {3, 6}]),
+    expect:equal(list:zip([5, 6], [1, 2, 3]), [{5, 1}, {6, 2}]),
+    expect:equal(list:zip([5, 6, 7], [1, 2]), [{5, 1}, {6, 2}]).
diff --git a/src/list.gleam b/src/list.gleam
index 83c22c4..5ea2ee3 100644
--- a/src/list.gleam
+++ b/src/list.gleam
@@ -4,7 +4,6 @@
 // TODO: intersperse
 // TODO: sort
 // TODO: unique
-// TODO: zip
 
 pub enum Empty =
   | Empty
@@ -177,3 +176,11 @@ pub fn any(list, f) {
       }
   }
 }
+
+pub fn zip(l1, l2) {
+  case {l1, l2} {
+    | {[], _} -> []
+    | {_, []} -> []
+    | {[x1 | rest1], [x2 | rest2] } -> [ {x1, x2} | zip(rest1, rest2) ]
+  }
+}
diff --git a/test/list_test.gleam b/test/list_test.gleam
index 2afd9e2..e7cd786 100644
--- a/test/list_test.gleam
+++ b/test/list_test.gleam
@@ -184,3 +184,20 @@ pub fn any_test() {
   list:any([], fn(_) { False })
   |> expect:equal(_, False)
 }
+
+pub fn zip_test() {
+  list:zip([], [1,2,3])
+  |> expect:equal(_, [])
+
+  list:zip([1,2], [])
+  |> expect:equal(_, [])
+
+  list:zip([1,2,3], [4,5,6])
+  |> expect:equal(_, [{1,4}, {2,5}, {3,6}])
+
+  list:zip([5,6], [1,2,3])
+  |> expect:equal(_, [{5,1}, {6,2}])
+
+  list:zip([5,6,7], [1,2])
+  |> expect:equal(_, [{5,1}, {6,2}])
+}