//erl[1,2|3] output for inspecting improper Erlang lists

1 files changed, 24 insertions, 8 deletions

diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index abb3b45..0d817fe 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -349,7 +349,10 @@ inspect(Binary) when is_binary(Binary) ->
             ["<<", lists:join(", ", Segments), ">>"]
     end;
 inspect(Elements) when is_list(Elements) ->
-    ["[", inspect_list(Elements), "]"];
+    case is_proper_list(Elements) of
+        true -> ["[", inspect_proper_list(Elements), "]"];
+        false -> ["//erl[", inspect_improper_list(Elements), "] %% improper list"]
+    end;
 inspect(Any) when is_tuple(Any) % Record constructors
   andalso is_atom(element(1, Any))
   andalso element(1, Any) =/= false
@@ -374,14 +377,27 @@ inspect(Any) when is_function(Any) ->
 inspect(Any) ->
     ["//erl(", io_lib:format("~p", [Any]), ")"].
 
-inspect_list([])  ->
+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(_NthCall, []) ->
     [];
-inspect_list([Head]) ->
-    [inspect(Head)];
-inspect_list([First | Rest]) ->
-    [inspect(First), <<", ">> | inspect_list(Rest)];
-inspect_list(ImproperTail) ->
-    [<<"..">>, inspect(ImproperTail)].
+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)].
 
 float_to_string(Float) when is_float(Float) ->
     erlang:iolist_to_binary(io_lib_format:fwrite_g(Float)).