From 5956ba6b38f56c4aa41f7216f7dabade368bb2f2 Mon Sep 17 00:00:00 2001 From: aarne Date: Sat, 3 Nov 2007 22:00:08 +0000 Subject: command language and gfcc term parser in bnfc --- src/GF/Command/ErrM.hs | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) create mode 100644 src/GF/Command/ErrM.hs (limited to 'src/GF/Command/ErrM.hs') diff --git a/src/GF/Command/ErrM.hs b/src/GF/Command/ErrM.hs new file mode 100644 index 000000000..b1f6329c2 --- /dev/null +++ b/src/GF/Command/ErrM.hs @@ -0,0 +1,26 @@ +-- BNF Converter: Error Monad +-- Copyright (C) 2004 Author: Aarne Ranta + +-- This file comes with NO WARRANTY and may be used FOR ANY PURPOSE. +module GF.Command.ErrM where + +-- the Error monad: like Maybe type with error msgs + +import Control.Monad (MonadPlus(..), liftM) + +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 >>= f = Bad s + +instance Functor Err where + fmap = liftM + +instance MonadPlus Err where + mzero = Bad "Err.mzero" + mplus (Bad _) y = y + mplus x _ = x -- cgit v1.2.3