{-# LANGUAGE CPP, NoImplicitPrelude, BangPatterns, PackageImports #-}

-- |
-- The Haskell 98 Prelude: a standard module imported by default
-- into all Haskell modules.  For more documentation, see the Haskell 98
-- Report <http://www.haskell.org/onlinereport/>.

module Prelude (

    -- * Standard types, classes and related functions

    -- ** Basic data types
    Bool(False, True),
    (&&), (||), not, otherwise,

    Maybe(Nothing, Just),
    maybe,

    Either(Left, Right),
    either,

    Ordering(LT, EQ, GT),
    Char, String,

    -- *** Tuples
    fst, snd, curry, uncurry,

#if defined(__NHC__)
    []((:), []),        -- Not legal Haskell 98;
                        -- ... available through built-in syntax
    module Data.Tuple,  -- Includes tuple types
    ()(..),             -- Not legal Haskell 98
    (->),               -- ... available through built-in syntax
#endif
#ifdef __HUGS__
    (:),                -- Not legal Haskell 98
#endif

    -- ** Basic type classes
    Eq((==), (/=)),
    Ord(compare, (<), (<=), (>=), (>), max, min),
    Enum(succ, pred, toEnum, fromEnum, enumFrom, enumFromThen,
         enumFromTo, enumFromThenTo),
    Bounded(minBound, maxBound),

    -- ** Numbers

    -- *** Numeric types
    Int, Integer, Float, Double,
    Rational,

    -- *** Numeric type classes
    Num((+), (-), (*), negate, abs, signum, fromInteger),
    Real(toRational),
    Integral(quot, rem, div, mod, quotRem, divMod, toInteger),
    Fractional((/), recip, fromRational),
    Floating(pi, exp, log, sqrt, (**), logBase, sin, cos, tan,
             asin, acos, atan, sinh, cosh, tanh, asinh, acosh, atanh),
    RealFrac(properFraction, truncate, round, ceiling, floor),
    RealFloat(floatRadix, floatDigits, floatRange, decodeFloat,
              encodeFloat, exponent, significand, scaleFloat, isNaN,
              isInfinite, isDenormalized, isIEEE, isNegativeZero, atan2),

    -- *** Numeric functions
    subtract, even, odd, gcd, lcm, (^), (^^),
    fromIntegral, realToFrac,

    -- ** Monads and functors
    Monad((>>=), (>>), return, fail),
    Functor(fmap),
    mapM, mapM_, sequence, sequence_, (=<<),

    -- ** Miscellaneous functions
    id, const, (.), flip, ($), until,
    asTypeOf, error, undefined,
    seq, ($!),

    -- * List operations
    map, (++), filter,
    head, last, tail, init, null, length, (!!),
    reverse,
    -- ** Reducing lists (folds)
    foldl, foldl1, foldr, foldr1,
    -- *** Special folds
    and, or, any, all,
    sum, product,
    concat, concatMap,
    maximum, minimum,
    -- ** Building lists
    -- *** Scans
    scanl, scanl1, scanr, scanr1,
    -- *** Infinite lists
    iterate, repeat, replicate, cycle,
    -- ** Sublists
    take, drop, splitAt, takeWhile, dropWhile, span, break,
    -- ** Searching lists
    elem, notElem, lookup,
    -- ** Zipping and unzipping lists
    zip, zip3, zipWith, zipWith3, unzip, unzip3,
    -- ** Functions on strings
    lines, words, unlines, unwords,

    -- * Converting to and from @String@
    -- ** Converting to @String@
    ShowS,
    Show(showsPrec, showList, show),
    shows,
    showChar, showString, showParen,
    -- ** Converting from @String@
    ReadS,
    Read(readsPrec, readList),
    reads, readParen, read, lex,

    -- * Basic Input and output
    IO,
    -- ** Simple I\/O operations
    -- All I/O functions defined here are character oriented.  The
    -- treatment of the newline character will vary on different systems.
    -- For example, two characters of input, return and linefeed, may
    -- read as a single newline character.  These functions cannot be
    -- used portably for binary I/O.
    -- *** Output functions
    putChar,
    putStr, putStrLn, print,
    -- *** Input functions
    getChar,
    getLine, getContents, interact,
    -- *** Files
    FilePath,
    readFile, writeFile, appendFile, readIO, readLn,
    -- ** Exception handling in the I\/O monad
    IOError, ioError, userError, catch

  ) where

#ifndef __HUGS__
import qualified "base" Control.Exception.Base as New (catch)
import "base" Control.Monad
import "base" System.IO
import "base" System.IO.Error (IOError, ioError, userError)
import "base" Data.List
import "base" Data.Either
import "base" Data.Maybe
import "base" Data.Tuple
#endif

#ifdef __GLASGOW_HASKELL__
import GHC.Base
-- import GHC.IO
-- import GHC.IO.Exception
import Text.Read
import GHC.Enum
import GHC.Num
import GHC.Real
import GHC.Float
import GHC.Show
import GHC.Err   ( undefined )
#endif

#ifdef __HUGS__
import Hugs.Prelude
#endif

#ifndef __HUGS__
infixr 0 $!
#endif

-- -----------------------------------------------------------------------------
-- Miscellaneous functions

-- | Strict (call-by-value) application, defined in terms of 'seq'.
($!)    :: (a -> b) -> a -> b
#ifdef __GLASGOW_HASKELL__
f $! x  = let !vx = x in f vx  -- see #2273
#elif !defined(__HUGS__)
f $! x  = x `seq` f x
#endif

#ifdef __HADDOCK__
-- | The value of @'seq' a b@ is bottom if @a@ is bottom, and otherwise
-- equal to @b@.  'seq' is usually introduced to improve performance by
-- avoiding unneeded laziness.
seq :: a -> b -> b
seq _ y = y
#endif

-- | The 'catch' function establishes a handler that receives any
-- 'IOError' raised in the action protected by 'catch'.
-- An 'IOError' is caught by
-- the most recent handler established by one of the exception handling
-- functions.  These handlers are
-- not selective: all 'IOError's are caught.  Exception propagation
-- must be explicitly provided in a handler by re-raising any unwanted
-- exceptions.  For example, in
--
-- > f = catch g (\e -> if IO.isEOFError e then return [] else ioError e)
--
-- the function @f@ returns @[]@ when an end-of-file exception
-- (cf. 'System.IO.Error.isEOFError') occurs in @g@; otherwise, the
-- exception is propagated to the next outer handler.
--
-- When an exception propagates outside the main program, the Haskell
-- system prints the associated 'IOError' value and exits the program.
--
-- Non-I\/O exceptions are not caught by this variant; to catch all
-- exceptions, use 'Control.Exception.catch' from "Control.Exception".
catch :: IO a -> (IOError -> IO a) -> IO a
catch = New.catch