Iron out the remaining issues with exception handling

Author: hmdne

app/ruby_engine.rb

@@ -12,7 +12,7 @@ def run(source)
   def run_with_writer(source, writer, &block)
     @writer = writer
     @dots = 0
-    run(source, &block)
+    run(source, &block).__await__
   end
 
   # Display a message while a block is being executed

app/ruby_engine/opal_webworker.rb

@@ -81,6 +81,8 @@ def initialize(version)
         super()
       end
 
+      attr_writer :writer
+
       def upload_opal_await(engine)
         engine.loading("downloading ruby") { upload_script_await("opal") }
         engine.loading("downloading ruby extras") { upload_script_await("opal/full") }
@@ -93,7 +95,7 @@ def upload_script_await(name)
       end
 
       def eval_ruby_await(ruby)
-        send_await(:eval, "var out = eval(Opal.compile(#{ruby.to_json})); out === Opal.nil ? '' : out.$to_s();")
+        send_await(:eval, "var out = eval(Opal.compile(#{ruby.to_json})); (out == null || out === Opal.nil) ? '' : out.$to_s();")
       end
 
       def prepare_stdio_await
@@ -126,7 +128,7 @@ def prepare_error_handler_await
       end
 
       def handle_error(err)
-        # @writer.log_error err
+        @writer.log_error err
       end
     end
 
@@ -144,6 +146,7 @@ def engine_id
 
     def run(source)
       worker = OpalWorker.new(@version)
+      worker.writer = @writer
 
       worker.upload_opal_await(self)
 
@@ -152,12 +155,14 @@ def run(source)
         worker.prepare_stdio_await
       end
 
-      yield(worker.eval_ruby_await(source))
+      retval = worker.eval_ruby_await(source)
 
       # Ensure the errors arrive
       worker.send_await(:nop)
 
       worker.close
+
+      yield(retval)
     end
   end
 end

app/try_ruby.rb

@@ -392,7 +392,7 @@ def eval_code(source)
   end
 
   def show_result(retval)
-    print_to_output(retval) if @output_buffer.length == 0 && !retval.empty?
+    print_to_output(retval) if @output_buffer.length == 0 && retval && !retval.empty?
 
     # Do not check the answer if there is no regexp matcher
     if @current_item && @current_item.answer