src/Text/PrettyPrint/HughesPJClass.hs

    #if __GLASGOW_HASKELL__ >= 701
    {-# LANGUAGE Safe #-}
    #endif

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Text.PrettyPrint.HughesPJClass
    -- Copyright   :  (c) Lennart Augustsson 2014
    -- License     :  BSD-style (see the file LICENSE)
    --
    -- Maintainer  :  David Terei <code@davidterei.com>
    -- Stability   :  stable
    -- Portability :  portable
    --
    -- Pretty printing class, simlar to 'Show' but nicer looking.
    --
    -- Note that the precedence level is a 'Rational' so there is an unlimited
    -- number of levels. This module re-exports 'Text.PrettyPrint.HughesPJ'.
    --
    -----------------------------------------------------------------------------

    module Text.PrettyPrint.HughesPJClass (
        -- * Pretty typeclass
        Pretty(..),

        PrettyLevel(..), prettyNormal,
        prettyShow, prettyParen,

        -- re-export HughesPJ
        module Text.PrettyPrint.HughesPJ
      ) where

    import Text.PrettyPrint.HughesPJ

    -- | Level of detail in the pretty printed output. Level 0 is the least
    -- detail.
    newtype PrettyLevel = PrettyLevel Int
      deriving (Eq, Ord, Show)

    -- | The "normal" (Level 0) of detail.
    prettyNormal :: PrettyLevel
    prettyNormal = PrettyLevel 0

    -- | Pretty printing class. The precedence level is used in a similar way as in
    -- the 'Show' class. Minimal complete definition is either 'pPrintPrec' or
    -- 'pPrint'.
    class Pretty a where
      pPrintPrec :: PrettyLevel -> Rational -> a -> Doc
      pPrintPrec _ _ = pPrint

      pPrint :: a -> Doc
      pPrint = pPrintPrec prettyNormal 0

      pPrintList :: PrettyLevel -> [a] -> Doc
      pPrintList l = brackets . fsep . punctuate comma . map (pPrintPrec l 0)

    #if __GLASGOW_HASKELL__ >= 708
      {-# MINIMAL pPrintPrec | pPrint #-}
    #endif

    -- | Pretty print a value with the 'prettyNormal' level.
    prettyShow :: (Pretty a) => a -> String
    prettyShow = render . pPrint

    pPrint0 :: (Pretty a) => PrettyLevel -> a -> Doc
    pPrint0 l = pPrintPrec l 0

    appPrec :: Rational
    appPrec = 10

    -- | Parenthesize an value if the boolean is true.
    {-# DEPRECATED prettyParen "Please use 'maybeParens' instead" #-}
    prettyParen :: Bool -> Doc -> Doc
    prettyParen = maybeParens

    -- Various Pretty instances
    instance Pretty Int where pPrint = int

    instance Pretty Integer where pPrint = integer

    instance Pretty Float where pPrint = float

    instance Pretty Double where pPrint = double

    instance Pretty () where pPrint _ = text "()"

    instance Pretty Bool where pPrint = text . show

    instance Pretty Ordering where pPrint = text . show

    instance Pretty Char where
      pPrint = char
      pPrintList _ = text . show

    instance (Pretty a) => Pretty (Maybe a) where
      pPrintPrec _ _ Nothing = text "Nothing"
      pPrintPrec l p (Just x) =
        prettyParen (p > appPrec) $ text "Just" <+> pPrintPrec l (appPrec+1) x

    instance (Pretty a, Pretty b) => Pretty (Either a b) where
      pPrintPrec l p (Left x) =
        prettyParen (p > appPrec) $ text "Left" <+> pPrintPrec l (appPrec+1) x
      pPrintPrec l p (Right x) =
        prettyParen (p > appPrec) $ text "Right" <+> pPrintPrec l (appPrec+1) x

    instance (Pretty a) => Pretty [a] where
      pPrintPrec l _ = pPrintList l

    instance (Pretty a, Pretty b) => Pretty (a, b) where
      pPrintPrec l _ (a, b) =
        parens $ fsep $ punctuate comma [pPrint0 l a, pPrint0 l b]

    instance (Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) where
      pPrintPrec l _ (a, b, c) =
        parens $ fsep $ punctuate comma [pPrint0 l a, pPrint0 l b, pPrint0 l c]

    instance (Pretty a, Pretty b, Pretty c, Pretty d) => Pretty (a, b, c, d) where
      pPrintPrec l _ (a, b, c, d) =
        parens $ fsep $ punctuate comma
          [pPrint0 l a, pPrint0 l b, pPrint0 l c, pPrint0 l d]

    instance (Pretty a, Pretty b, Pretty c, Pretty d, Pretty e) => Pretty (a, b, c, d, e) where
      pPrintPrec l _ (a, b, c, d, e) =
        parens $ fsep $ punctuate comma
          [pPrint0 l a, pPrint0 l b, pPrint0 l c, pPrint0 l d, pPrint0 l e]

    instance (Pretty a, Pretty b, Pretty c, Pretty d, Pretty e, Pretty f) => Pretty (a, b, c, d, e, f) where
      pPrintPrec l _ (a, b, c, d, e, f) =
        parens $ fsep $ punctuate comma
          [pPrint0 l a, pPrint0 l b, pPrint0 l c,
            pPrint0 l d, pPrint0 l e, pPrint0 l f]

    instance (Pretty a, Pretty b, Pretty c, Pretty d, Pretty e, Pretty f, Pretty g) =>
             Pretty (a, b, c, d, e, f, g) where
      pPrintPrec l _ (a, b, c, d, e, f, g) =
        parens $ fsep $ punctuate comma
          [pPrint0 l a, pPrint0 l b, pPrint0 l c,
            pPrint0 l d, pPrint0 l e, pPrint0 l f, pPrint0 l g]

    instance (Pretty a, Pretty b, Pretty c, Pretty d, Pretty e, Pretty f, Pretty g, Pretty h) =>
             Pretty (a, b, c, d, e, f, g, h) where
      pPrintPrec l _ (a, b, c, d, e, f, g, h) =
        parens $ fsep $ punctuate comma
          [pPrint0 l a, pPrint0 l b, pPrint0 l c,
            pPrint0 l d, pPrint0 l e, pPrint0 l f, pPrint0 l g, pPrint0 l h]