Text.hs

-- |
-- Module      :  Data.Attoparsec.Text
-- Copyright   :  Felipe Lessa 2010-2011, Bryan O'Sullivan 2007-2010
-- License     :  BSD3
--
-- Maintainer  :  felipe.lessa@gmail.com
-- Stability   :  experimental
-- Portability :  unknown
--
-- Simple, efficient combinator parsing for 'T.Text' strings,
-- loosely based on the Parsec library.

module Data.Attoparsec.Text
    (
    -- * Differences from Parsec
    -- $parsec

    -- * Incremental input
    -- $incremental

    -- * Performance considerations
    -- $performance

    -- * Parser types
      I.Parser
    , Result(..)

    -- ** Typeclass instances
    -- $instances

    -- * Running parsers
    , parse
    , feed
    , I.parseOnly
    , parseWith
    , parseTest

    -- ** Result conversion
    , maybeResult
    , eitherResult

    -- * Combinators
    , (I.<?>)
    , I.try
    , module Data.Attoparsec.Combinator

    -- * Parsing individual characters
    , I.char
    , I.anyChar
    , I.notChar
    , I.satisfy
    , I.satisfyWith
    , I.skip

    -- ** Special character parsers
    -- $specialcharparsers
    , I.digit
    , I.letter
    , I.space

    -- ** Character classes
    , I.inClass
    , I.notInClass

    -- * Efficient string handling
    , I.string
    , I.skipSpace
    , I.skipWhile
    , I.take
    , I.scan
    , I.takeWhile
    , I.takeWhile1
    , I.takeTill

    -- ** Consume all remaining input
    , I.takeText
    , I.takeLazyText

    -- * Text parsing
    , I.endOfLine

    -- * Numeric parsers
    , I.decimal
    , I.hexadecimal
    , I.signed
    , I.double
    , I.rational

    -- * State observation and manipulation functions
    , I.endOfInput
    , I.atEnd

    -- * Applicative specializations
    -- $applicative
    , (<*.)
    , (.*>)
    ) where

import Control.Applicative (Applicative, (<*), (*>))
import Data.Attoparsec.Combinator
import qualified Data.Attoparsec.Text.Internal as I
import qualified Data.Text as T
import Data.Attoparsec.Text.Internal (Result(..), parse)

-- $parsec
--
-- Compared to Parsec 3, @attoparsec-text@ makes several
-- tradeoffs.  It is not intended for, or ideal for, all possible
-- uses.
--
-- * While @attoparsec-text@ can consume input incrementally,
--   Parsec cannot.  Incremental input is a huge deal for
--   efficient and secure network and system programming, since
--   it gives much more control to users of the library over
--   matters such as resource usage and the I/O model to use.
--
-- * Much of the performance advantage of @attoparsec-text@ is
--   gained via high-performance parsers such as 'I.takeWhile'
--   and 'I.string'.  If you use complicated combinators that
--   return lists of characters, there is less performance
--   difference between the two libraries.
--
-- * Unlike Parsec 3, @attoparsec-text@ does not support being
--   used as a monad transformer.
--
-- * @attoparsec-text@ is specialised to deal only with strict
--   'T.Text' input.  Efficiency concernts rule out both lists
--   and lazy texts.  The usual use for lazy texts would be to
--   allow consumption of very large input without a large
--   footprint.  For this need, @attoparsec-text@'s incremental
--   input provides an excellent substitute, with much more
--   control over when input takes place.  If you must use lazy
--   texts, see the 'Lazy' module, which feeds lazy chunks to a
--   regular parser.
--
-- * Parsec parsers can produce more helpful error messages than
--   @attoparsec-text@ parsers.  This is a matter of focus:
--   @attoparsec-text@ avoids the extra book-keeping in favour of
--   higher performance.

-- $incremental
--
-- @attoparsec-text@ supports incremental input, meaning that you
-- can feed it a text that represents only part of the
-- expected total amount of data to parse. If your parser reaches
-- the end of a fragment of input and could consume more input,
-- it will suspend parsing and return a 'Partial' continuation.
--
-- Supplying the 'Partial' continuation with another text will
-- resume parsing at the point where it was suspended. You must be
-- prepared for the result of the resumed parse to be another
-- 'Partial' continuation.
--
-- To indicate that you have no more input, supply the 'Partial'
-- continuation with an empty text.
--
-- Remember that some parsing combinators will not return a result
-- until they reach the end of input.  They may thus cause 'Partial'
-- results to be returned.
--
-- If you do not need support for incremental input, consider using
-- the 'I.parseOnly' function to run your parser.  It will never
-- prompt for more input.

-- $performance
--
-- To actually achieve high performance, there are a few guidelines
-- that it is useful to follow.
--
-- Use the 'T.Text'-oriented parsers whenever possible,
-- e.g. 'I.takeWhile1' instead of 'many1' 'I.anyChar'.  There is
-- about a factor of 100 difference in performance between the
-- two kinds of parser.
--
-- For very simple character-testing predicates, write them by
-- hand instead of using 'I.inClass' or 'I.notInClass'.  For
-- instance, both of these predicates test for an end-of-line
-- character, but the first is much faster than the second:
--
-- >endOfLine_fast c = w == '\r' || c == '\n'
-- >endOfLine_slow   = inClass "\r\n"
--
-- Make active use of benchmarking and profiling tools to measure,
-- find the problems with, and improve the performance of your parser.

-- $instances
--
-- The 'I.Parser' type is an instance of the following classes:
--
-- * 'Monad', where 'fail' throws an exception (i.e. fails) with an
--   error message.
--
-- * 'Functor' and 'Applicative', which follow the usual definitions.
--
-- * 'MonadPlus', where 'mzero' fails (with no error message) and
--   'mplus' executes the right-hand parser if the left-hand one
--   fails.
--
-- * 'Alternative', which follows 'MonadPlus'.
--
-- The 'Result' type is an instance of 'Functor', where 'fmap'
-- transforms the value in a 'Done' result.

-- | If a parser has returned a 'Partial' result, supply it with more
-- input.
feed :: Result r -> T.Text -> Result r
feed f@(Fail _ _ _) _ = f
feed (Partial k) d    = k d
feed (Done bs r) d    = Done (T.append bs d) r
{-# INLINE feed #-}

-- | Run a parser and print its result to standard output.
parseTest :: (Show a) => I.Parser a -> T.Text -> IO ()
parseTest p s = print (parse p s)

-- | Run a parser with an initial input string, and a monadic action
-- that can supply more input if needed.
parseWith :: Monad m =>
             (m T.Text)
          -- ^ An action that will be executed to provide the parser
          -- with more input, if necessary.  The action must return an
          -- 'T.empty' string when there is no more input available.
          -> I.Parser a
          -> T.Text
          -- ^ Initial input for the parser.
          -> m (Result a)
parseWith refill p s = step $ parse p s
  where step (Partial k) = (step . k) =<< refill
        step r           = return r

-- | Convert a 'Result' value to a 'Maybe' value. A 'Partial' result
-- is treated as failure.
maybeResult :: Result r -> Maybe r
maybeResult (Done _ r) = Just r
maybeResult _          = Nothing

-- | Convert a 'Result' value to an 'Either' value. A 'Partial' result
-- is treated as failure.
eitherResult :: Result r -> Either String r
eitherResult (Done _ r)     = Right r
eitherResult (Fail _ _ msg) = Left msg
eitherResult _              = Left "Result: incomplete input"

-- $specialcharparsers
--
-- Special parser for characters.  Unlike the original
-- @attoparsec@ package, these parsers do work correctly for all
-- encodings.  Internally "Data.Char" module is used.


-- $applicative
--
-- We provide specializations of @\<*@ and @*\>@ as @\<*.@ and
-- @.*\>@, respectively.  Together with @IsString@ instance of
-- 'I.Parser', you may write parsers applicatively more easily.
-- For example:
--
-- > paren p = "(" .*> p <*. ")"
--
-- instead of the more verbose
--
-- > paren p = string "(" *> p <* string ")"

-- | Same as @Applicative@'s @\<*@ but specialized to 'T.Text'
-- on the second argument.
(<*.) :: Applicative f => f a -> f T.Text -> f a
(<*.) = (<*)

-- | Same as @Applicative@'s @*\>@ but specialized to 'T.Text'
-- on the first argument.
(.*>) :: Applicative f => f T.Text -> f a -> f a
(.*>) = (*>)