Custom error payloads example, using a "context" struct

[joshring]

struct ParseContext
{
   ParseError last_parse_error;
   ...
}


fn String! parse_string(ParseContext* c)
{
   ...
   if (something_bad) 
   {
      c.last_parse_error = new_parse_error("Something Bad Happened at line %d", context.line);
      return ParseError.SOMETHING_BAD?;
   }
}

In some cases one could imagine it looking like this:

fn String! parse_string(ParseContext* c)
{
   ...
   if (something_bad) 
   {
      return c.add_error(SOMETHING_BAD, "Something Bad Happened at line %d", context.line);
   }
}

And it would be equivalent to the code above.