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--------------------------------------------------------------------------------
-- | This library provides a type and combinators for show functions using
--   functional lists.
--
-- Author:  Bjoern Peemoeller
-- Version: April 2016
--------------------------------------------------------------------------------
module Text.Show ( ShowS
                 , showString, showChar, showParen, shows
                 ) where

-- | The type synonym `ShowS` represents strings as difference lists.
--   Composing functions of this type allows concatenation of lists
--   in constant time.
type ShowS = String -> String

-- | Prepend a string
showString :: String -> ShowS
showString s = (s ++)

-- | Prepend a single character
showChar :: Char -> ShowS
showChar c = (c:)

-- | Surround the inner show function with parentheses if the first argument
--   evaluates to `True`.
showParen  :: Bool -> ShowS -> ShowS
showParen True  s = showChar '(' . s . showChar ')'
showParen False s = s

-- | Convert a value to `ShowS` using the standard show function.
shows :: Show a => a -> ShowS
shows = showString . show