single pass proper/improper list inspection

2 files changed, 17 insertions, 26 deletions

diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index 8417e7c..c06854a 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -348,10 +348,10 @@ inspect(Binary) when is_binary(Binary) ->
             Segments = [erlang:integer_to_list(X) || <<X>> <= Binary],
             ["<<", lists:join(", ", Segments), ">>"]
     end;
-inspect(Elements) when is_list(Elements) ->
-    case is_proper_list(Elements) of
-        true -> ["[", inspect_proper_list(Elements), "]"];
-        false -> ["//erl[", inspect_improper_list(Elements), "] %% improper list"]
+inspect(List) when is_list(List) ->
+    case inspect_list(firstCall, properList, List) of
+        {properList, Elements} -> ["[", Elements, "]"];
+        {improperList, Elements} -> ["//erl[", Elements, "] %% improper list"]
     end;
 inspect(Any) when is_tuple(Any) % Record constructors
   andalso is_atom(element(1, Any))
@@ -377,25 +377,18 @@ inspect(Any) when is_function(Any) ->
 inspect(Any) ->
     ["//erl(", io_lib:format("~p", [Any]), ")"].
 
-is_proper_list([])  ->
-    true;
-is_proper_list([_Head | Tail]) ->
-  is_proper_list(Tail);
-is_proper_list(ImproperTail) when not is_list(ImproperTail) ->
-    false.
-
-inspect_proper_list(List) ->
-    lists:join(<<", ">>, lists:map(fun inspect/1, List)).
-
-inspect_improper_list(Elements) ->
-	do_inspect_improper_list(firstCall, Elements).
-
-do_inspect_improper_list(firstCall, [First | Rest]) ->
-    [inspect(First) | do_inspect_improper_list(nthCall, Rest)];
-do_inspect_improper_list(nthCall, [First | Rest]) ->
-    [ <<",">>, inspect(First) | do_inspect_improper_list(nthCall, Rest)];
-do_inspect_improper_list(nthCall, ImproperTail) ->
-    [<<"|">>, inspect(ImproperTail)].
+inspect_list(_recursionCount, properList, []) ->
+    {properList, []};
+inspect_list(firstCall, properList, [Head]) ->
+    {properList, [inspect(Head)]};
+inspect_list(firstCall, properList, [First | Rest]) ->
+    {ListKind, Elements} = inspect_list(nthCall, properList, Rest),
+    {ListKind, [inspect(First) | Elements]};
+inspect_list(nthCall, properList, [First | Rest]) ->
+    {ListKind, Elements} = inspect_list(nthCall, properList, Rest),
+    {ListKind, [<<", ">>, inspect(First) | Elements]};
+inspect_list(nthCall, properList, ImproperTail) ->
+    {improperList, [<<" | ">>, inspect(ImproperTail)]}.
 
 float_to_string(Float) when is_float(Float) ->
     erlang:iolist_to_binary(io_lib_format:fwrite_g(Float)).
diff --git a/test/gleam/string_test.gleam b/test/gleam/string_test.gleam
index b025f5c..d817a35 100644
--- a/test/gleam/string_test.gleam
+++ b/test/gleam/string_test.gleam
@@ -791,12 +791,10 @@ if erlang {
     |> string.inspect()
     |> should.equal("\"abc\"")
   }
-}
 
-if erlang {
   pub fn improper_list_inspect_test() {
     let list = improper_list_append(1, 2, 3)
-    assert "//erl[1,2|3] %% improper list" = string.inspect(list)
+    assert "//erl[1, 2 | 3] %% improper list" = string.inspect(list)
   }
 
   // Warning: The type of this function is incorrect