Change Result Error type to String

and add some useful error messages.

2 files changed, 6 insertions, 8 deletions

diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index 4512c8a..0660a67 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -49,5 +49,5 @@ pub fn list(from dynamic, containing decoder_type) {
 pub external fn field(from: Dynamic, named: a) -> Result(Dynamic, String)
   = "gleam_stdlib" "decode_field"
 
-pub external fn element(from: Dynamic, position: Int) -> Result(Dynamic, Nil)
+pub external fn element(from: Dynamic, position: Int) -> Result(Dynamic, String)
   = "gleam_stdlib" "decode_element"
diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index abfdfbb..f963716 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -70,17 +70,15 @@ decode_field(Data, Key) ->
       decode_error_msg(io_lib:format("a map with key `~p`", [Key]), Data)
   end.
 
-decode_element(Data, Position) ->
+decode_element(Data, Position) when is_tuple(Data) ->
   case catch element(Position + 1, Data) of
     {'EXIT', _Reason} ->
-      {error, nil};
+      {error, "Element position is out-of-bounds"};
 
     Value ->
-      {ok, Value};
-
-    _ ->
-      {error, nil}
-  end.
+      {ok, Value}
+  end;
+decode_element(Data, Position) -> decode_error_msg("a Tuple", Data).
 
 parse_int(String) ->
   case string:to_integer(binary:bin_to_list(String)) of