{-
    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"]