Hi, I'm using the Happy parser, and I've threaded a Success/Failure monad-like thing through it so that if the parse succeeds, Success AST (AST is the datatype I want to turn my tokens into) is returned and if it fails, Fail String is returned (in a similar manner to how such threading is described in the Happy Documentation). That is, data SorF a = Succeed a | Fail String. Now, if the input is valid, I get the correct result (namely Success AST). If invalid input is given (ie the wrong token is encountered), happyError is triggered correctly, and and a Fail String is returned. However, if incomplete info is given (let's say a rule is expecting two tokens, and only one is read before the end of input), the parser generated by happy throws error("Reading EOF"). I have defined happyError on both the empty list of tokens, and the non-empty list as returning a Fail String. I'm stumped as to why I get this error. Any advice? Best, Mike.