{-
BNF Converter: Haskell error monad
Copyright (C) 2004-2007 Author: Markus Forberg, Peter Gammie,
Aarne Ranta, Björn Bringert
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
-}
module BNFC.Backend.Haskell.MkErrM where
errM :: String -> b -> String
errM errMod _ =
unlines
["-- BNF Converter: Error Monad"
,"-- Copyright (C) 2004 Author: Aarne Ranta"
,""
,"-- This file comes with NO WARRANTY and may be used FOR ANY PURPOSE."
,"module " ++ errMod ++ " where"
,""
,"-- the Error monad: like Maybe type with error msgs"
,""
,"import Control.Monad (MonadPlus(..), liftM)"
,"import Control.Applicative (Applicative(..), Alternative(..))"
,""
,"data Err a = Ok a | Bad String"
," deriving (Read, Show, Eq, Ord)"
,""
,"instance Monad Err where"
," return = Ok"
," fail = Bad"
," Ok a >>= f = f a"
," Bad s >>= _ = Bad s"
,""
,"instance Applicative Err where"
," pure = Ok"
," (Bad s) <*> _ = Bad s"
," (Ok f) <*> o = liftM f o"
,""
,""
,"instance Functor Err where"
," fmap = liftM"
,""
,"instance MonadPlus Err where"
," mzero = Bad \"Err.mzero\""
," mplus (Bad _) y = y"
," mplus x _ = x"
,""
,"instance Alternative Err where"
," empty = mzero"
," (<|>) = mplus"]