list:strict_zip (#167)

5 files changed, 46 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2672166..91d8232 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 a `range` function.
+- The `list` module gains `range`, and `strict_zip` functions.
 
 ## v0.1.2 - 2019-04-25
 
diff --git a/gen/src/list.erl b/gen/src/list.erl
index 85df70e..3170ec2 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, intersperse/2, at/2, unique/1, sort/1, range/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]).
 
 length(A) ->
     erlang:length(A).
@@ -226,6 +226,15 @@ zip(L1, L2) ->
             [{X1, X2} | zip(Rest1, Rest2)]
     end.
 
+strict_zip(L1, L2) ->
+    case length(L1) =:= length(L2) of
+        true ->
+            {ok, zip(L1, L2)};
+
+        false ->
+            {error, length_mismatch}
+    end.
+
 intersperse(List, Elem) ->
     case List of
         [] ->
diff --git a/gen/test/list_test.erl b/gen/test/list_test.erl
index ca76423..20c1d1c 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, intersperse_test/0, at_test/0, unique_test/0, sort_test/0, index_map_test/0, range_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]).
 
 length_test() ->
     expect:equal(list:length([]), 0),
@@ -111,6 +111,13 @@ zip_test() ->
     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}]).
 
+strict_zip_test() ->
+    expect:is_error(list:strict_zip([], [1, 2, 3])),
+    expect:is_error(list:strict_zip([1, 2], [])),
+    expect:equal(list:zip([1, 2, 3], [4, 5, 6]), [{1, 4}, {2, 5}, {3, 6}]),
+    expect:is_error(list:strict_zip([5, 6], [1, 2, 3])),
+    expect:is_error(list:strict_zip([5, 6, 7], [1, 2])).
+
 intersperse_test() ->
     expect:equal(list:intersperse([1, 2, 3], 4), [1, 4, 2, 4, 3]),
     expect:equal(list:intersperse([], 2), []).
diff --git a/src/list.gleam b/src/list.gleam
index dd8fb8a..288d971 100644
--- a/src/list.gleam
+++ b/src/list.gleam
@@ -7,6 +7,9 @@ pub enum Empty =
 pub enum NotFound =
   | NotFound
 
+pub enum LengthMismatch =
+  | LengthMismatch
+
 // Using the Erlang C BIF implementation.
 //
 pub external fn length(List(a)) -> Int = "erlang" "length"
@@ -192,6 +195,13 @@ pub fn zip(l1, l2) {
   }
 }
 
+pub fn strict_zip(l1, l2) {
+  case length(l1) == length(l2) {
+  | True -> Ok(zip(l1, l2))
+  | False -> Error(LengthMismatch)
+  }
+}
+
 pub fn intersperse(list, elem) {
   case list {
     | [] -> []
diff --git a/test/list_test.gleam b/test/list_test.gleam
index 81f2427..779ba7b 100644
--- a/test/list_test.gleam
+++ b/test/list_test.gleam
@@ -204,6 +204,23 @@ pub fn zip_test() {
   |> expect:equal(_, [{5, 1}, {6, 2}])
 }
 
+pub fn strict_zip_test() {
+  list:strict_zip([], [1, 2, 3])
+  |> expect:is_error
+
+  list:strict_zip([1, 2], [])
+  |> expect:is_error
+
+  list:zip([1, 2, 3], [4, 5, 6])
+  |> expect:equal(_, [{1, 4}, {2, 5}, {3, 6}])
+
+  list:strict_zip([5, 6], [1, 2, 3])
+  |> expect:is_error
+
+  list:strict_zip([5, 6, 7], [1, 2])
+  |> expect:is_error
+}
+
 pub fn intersperse_test() {
   list:intersperse([1, 2, 3], 4)
   |> expect:equal(_, [1, 4, 2, 4, 3])