{-
Copyright 2010-2011 Mario Blazevic
This file is part of the Streaming Component Combinators (SCC) project.
The SCC project 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 3 of the License, or (at your option) any later
version.
SCC 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 SCC. If not, see
.
-}
-- | This module defines incremental parsers.
--
-- The exported 'Parser' type can provide partial parsing results from partial input, as long as the output is a
-- 'Monoid'. Construct a parser using the primitives and combinators, supply it with input using functions 'feed' and
-- 'feedEof', and extract the parsed output using 'results'.
--
-- Implementation is based on Brzozowski derivatives.
{-# LANGUAGE EmptyDataDecls, FlexibleInstances #-}
module Text.ParserCombinators.Incremental.LeftBiasedLocal (
module Text.ParserCombinators.Incremental,
Parser, LeftBiasedLocal, leftmost
)
where
import Control.Applicative (Alternative (empty, (<|>)))
import Control.Monad (MonadPlus (mzero, mplus))
import Data.Monoid (Monoid)
import Text.ParserCombinators.Incremental hiding (Parser)
import qualified Text.ParserCombinators.Incremental as Incremental (Parser)
-- | An empty type to specialize 'Parser' for the left-biased 'Alternative' instance.
data LeftBiasedLocal
type Parser s r = Incremental.Parser LeftBiasedLocal s r
-- | Left-biased choice. The right parser is used only if the left one utterly fails.
instance Monoid s => Alternative (Incremental.Parser LeftBiasedLocal s) where
empty = failure
p1 <|> p2 = p1 <<|> p2
-- | The 'MonadPlus' instances are the same as the 'Alternative' instances.
instance Monoid s => MonadPlus (Incremental.Parser LeftBiasedLocal s) where
mzero = failure
mplus = (<|>)
leftmost :: Parser s r -> Incremental.Parser a s r
leftmost p = mapType leftmost p