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+%%---------------------------------------------------------------------------
+%% From: Nicolas Tranger <[email protected]>
+%% Date: 10/11/2110
+%%
+%% After adding spec statements to my module, Dialyzer failed on execution
+%% though. I've been trying to create a minimal reproducible case and
+%% reduced the code to something similar of about 80 LOC.  As noted in the
+%% comments, commenting out some lines makes Dialyzer parse and analyze
+%% the file correctly.  The code executes correctly and as expected.
+%%
+%% I'm not sure what causes the issue. parse_result is polymorphic in its
+%% return type, but statically typed based on the type of the 3th argument
+%% (well, that's how I see things from a Haskell background).
+%%---------------------------------------------------------------------------
+%% This was a bug in erl_types:t_subtract/2 which was not handling the case
+%% of free variables in prameterized types. Fixed 15/10/2010.
+%%---------------------------------------------------------------------------
+-module(param_types_crash).
+
+-export([test/0]).
+
+-type socket_error() :: 'connection_closed' | 'timeout'.
+-type app_error() :: 'no_magic' | 'unknown_failure'.
+
+-type resulthandler_result(T) :: {'ok', T} | socket_error() | app_error().
+-type resulthandler(T) :: fun((binary()) -> resulthandler_result(T)).
+
+test() ->
+  Data = <<0:32/little-unsigned, 1:8/little, 1:8/little-unsigned>>,
+  case parse_result(Data, get_option(fun get_bool/1)) of
+	%% Removing the next 2 lines makes
+	%% dialyzer param_types_crash.erl -Wunmatched_returns -Wunderspecs
+	%% succeed. With these lines, it fails.
+	{ok, none} -> none;
+	{ok, {some, Value}} -> Value;
+	Reply -> {error, Reply}
+  end.
+
+-spec parse_result(binary(), resulthandler(T)) -> resulthandler_result(T).
+parse_result(<<ResultCode:32/little-unsigned, Rest/binary>>, ResultHandler) ->
+  case ResultCode of
+	0 -> ResultHandler(Rest);
+	1 -> no_magic;
+	2 -> unknown_failure
+  end.
+
+-spec get_bool(binary()) -> {'ok', boolean()} | socket_error().
+get_bool(Data) ->
+  case get_data(Data, 1, size(Data)) of
+    {<<Value:8/little-unsigned>>, <<>>} -> {ok, (Value =:= 1)};
+    Other -> Other
+  end.
+
+-spec get_option(resulthandler(T)) -> resulthandler('none' | {'some', T}).
+get_option(Fun) ->
+  fun(Data) ->
+      case get_data(Data, 1, size(Data)) of
+	{<<HasValue:8/little>>, Rest} ->
+	  case HasValue of
+	    0 -> {ok, none};
+	    1 -> {ok, Value} = Fun(Rest),
+		 {ok, {some, Value}}
+	   end;
+	Other -> Other
+      end
+    end.
+
+-spec get_data(binary(), non_neg_integer(), non_neg_integer()) ->
+	{binary(), binary()} | socket_error().
+get_data(Data, Length, Received) when Length > Received ->
+    case Data of
+      <<>> -> connection_closed;
+      _ -> timeout
+    end;
+get_data(Data, Length, _) ->
+    <<Bin:Length/binary, Rest/binary>> = Data,
+    {Bin, Rest}.