GHC/Show.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE CPP, NoImplicitPrelude, BangPatterns, StandaloneDeriving,
                 MagicHash, UnboxedTuples #-}
    {-# OPTIONS_HADDOCK hide #-}

    #include "MachDeps.h"
    #if SIZEOF_HSWORD == 4
    #define DIGITS       9
    #define BASE         1000000000
    #elif SIZEOF_HSWORD == 8
    #define DIGITS       18
    #define BASE         1000000000000000000
    #else
    #error Please define DIGITS and BASE
    -- DIGITS should be the largest integer such that
    --     10^DIGITS < 2^(SIZEOF_HSWORD * 8 - 1)
    -- BASE should be 10^DIGITS. Note that ^ is not available yet.
    #endif

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.Show
    -- Copyright   :  (c) The University of Glasgow, 1992-2002
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  cvs-ghc@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable (GHC Extensions)
    --
    -- The 'Show' class, and related operations.
    --
    -----------------------------------------------------------------------------

    module GHC.Show
            (
            Show(..), ShowS,

            -- Instances for Show: (), [], Bool, Ordering, Int, Char

            -- Show support code
            shows, showChar, showString, showMultiLineString,
            showParen, showList__, showCommaSpace, showSpace,
            showLitChar, showLitString, protectEsc,
            intToDigit, showSignedInt,
            appPrec, appPrec1,

            -- Character operations
            asciiTab,
      )
            where

    import GHC.Base
    import GHC.List ((!!), foldr1, break)
    import GHC.Num
    import GHC.Stack.Types

    -- | The @shows@ functions return a function that prepends the
    -- output 'String' to an existing 'String'.  This allows constant-time
    -- concatenation of results using function composition.
    type ShowS = String -> String

    -- | Conversion of values to readable 'String's.
    --
    -- Derived instances of 'Show' have the following properties, which
    -- are compatible with derived instances of 'Text.Read.Read':
    --
    -- * The result of 'show' is a syntactically correct Haskell
    --   expression containing only constants, given the fixity
    --   declarations in force at the point where the type is declared.
    --   It contains only the constructor names defined in the data type,
    --   parentheses, and spaces.  When labelled constructor fields are
    --   used, braces, commas, field names, and equal signs are also used.
    --
    -- * If the constructor is defined to be an infix operator, then
    --   'showsPrec' will produce infix applications of the constructor.
    --
    -- * the representation will be enclosed in parentheses if the
    --   precedence of the top-level constructor in @x@ is less than @d@
    --   (associativity is ignored).  Thus, if @d@ is @0@ then the result
    --   is never surrounded in parentheses; if @d@ is @11@ it is always
    --   surrounded in parentheses, unless it is an atomic expression.
    --
    -- * If the constructor is defined using record syntax, then 'show'
    --   will produce the record-syntax form, with the fields given in the
    --   same order as the original declaration.
    --
    -- For example, given the declarations
    --
    -- > infixr 5 :^:
    -- > data Tree a =  Leaf a  |  Tree a :^: Tree a
    --
    -- the derived instance of 'Show' is equivalent to
    --
    -- > instance (Show a) => Show (Tree a) where
    -- >
    -- >        showsPrec d (Leaf m) = showParen (d > app_prec) $
    -- >             showString "Leaf " . showsPrec (app_prec+1) m
    -- >          where app_prec = 10
    -- >
    -- >        showsPrec d (u :^: v) = showParen (d > up_prec) $
    -- >             showsPrec (up_prec+1) u .
    -- >             showString " :^: "      .
    -- >             showsPrec (up_prec+1) v
    -- >          where up_prec = 5
    --
    -- Note that right-associativity of @:^:@ is ignored.  For example,
    --
    -- * @'show' (Leaf 1 :^: Leaf 2 :^: Leaf 3)@ produces the string
    --   @\"Leaf 1 :^: (Leaf 2 :^: Leaf 3)\"@.

    class  Show a  where
        {-# MINIMAL showsPrec | show #-}

        -- | Convert a value to a readable 'String'.
        --
        -- 'showsPrec' should satisfy the law
        --
        -- > showsPrec d x r ++ s  ==  showsPrec d x (r ++ s)
        --
        -- Derived instances of 'Text.Read.Read' and 'Show' satisfy the following:
        --
        -- * @(x,\"\")@ is an element of
        --   @('Text.Read.readsPrec' d ('showsPrec' d x \"\"))@.
        --
        -- That is, 'Text.Read.readsPrec' parses the string produced by
        -- 'showsPrec', and delivers the value that 'showsPrec' started with.

        showsPrec :: Int    -- ^ the operator precedence of the enclosing
                            -- context (a number from @0@ to @11@).
                            -- Function application has precedence @10@.
                  -> a      -- ^ the value to be converted to a 'String'
                  -> ShowS

        -- | A specialised variant of 'showsPrec', using precedence context
        -- zero, and returning an ordinary 'String'.
        show      :: a   -> String

        -- | The method 'showList' is provided to allow the programmer to
        -- give a specialised way of showing lists of values.
        -- For example, this is used by the predefined 'Show' instance of
        -- the 'Char' type, where values of type 'String' should be shown
        -- in double quotes, rather than between square brackets.
        showList  :: [a] -> ShowS

        showsPrec _ x s = show x ++ s
        show x          = shows x ""
        showList ls   s = showList__ shows ls s

    showList__ :: (a -> ShowS) ->  [a] -> ShowS
    showList__ _     []     s = "[]" ++ s
    showList__ showx (x:xs) s = '[' : showx x (showl xs)
      where
        showl []     = ']' : s
        showl (y:ys) = ',' : showx y (showl ys)

    appPrec, appPrec1 :: Int
            -- Use unboxed stuff because we don't have overloaded numerics yet
    appPrec = I# 10#        -- Precedence of application:
                            --   one more than the maximum operator precedence of 9
    appPrec1 = I# 11#       -- appPrec + 1

    --------------------------------------------------------------
    -- Simple Instances
    --------------------------------------------------------------

    deriving instance Show ()

    -- | @since 2.01
    instance Show a => Show [a]  where
      {-# SPECIALISE instance Show [String] #-}
      {-# SPECIALISE instance Show [Char] #-}
      {-# SPECIALISE instance Show [Int] #-}
      showsPrec _         = showList

    deriving instance Show Bool
    deriving instance Show Ordering

    -- | @since 2.01
    instance  Show Char  where
        showsPrec _ '\'' = showString "'\\''"
        showsPrec _ c    = showChar '\'' . showLitChar c . showChar '\''

        showList cs = showChar '"' . showLitString cs . showChar '"'

    -- | @since 2.01
    instance Show Int where
        showsPrec = showSignedInt

    -- | @since 2.01
    instance Show Word where
        showsPrec _ (W# w) = showWord w

    showWord :: Word# -> ShowS
    showWord w# cs
     | isTrue# (w# `ltWord#` 10##) = C# (chr# (ord# '0'# +# word2Int# w#)) : cs
     | otherwise = case chr# (ord# '0'# +# word2Int# (w# `remWord#` 10##)) of
                   c# ->
                       showWord (w# `quotWord#` 10##) (C# c# : cs)

    deriving instance Show a => Show (Maybe a)

    -- | @since 2.01
    instance Show TyCon where
      showsPrec p (TyCon _ _ _ tc_name _ _) = showsPrec p tc_name

    -- | @since 4.9.0.0
    instance Show TrName where
      showsPrec _ (TrNameS s) = showString (unpackCString# s)
      showsPrec _ (TrNameD s) = showString s

    -- | @since 4.9.0.0
    instance Show Module where
      showsPrec _ (Module p m) = shows p . (':' :) . shows m

    -- | @since 4.9.0.0
    instance Show CallStack where
      showsPrec _ = shows . getCallStack

    deriving instance Show SrcLoc

    --------------------------------------------------------------
    -- Show instances for the first few tuple
    --------------------------------------------------------------

    -- The explicit 's' parameters are important
    -- Otherwise GHC thinks that "shows x" might take a lot of work to compute
    -- and generates defns like
    --      showsPrec _ (x,y) = let sx = shows x; sy = shows y in
    --                          \s -> showChar '(' (sx (showChar ',' (sy (showChar ')' s))))

    -- | @since 2.01
    instance  (Show a, Show b) => Show (a,b)  where
      showsPrec _ (a,b) s = show_tuple [shows a, shows b] s

    -- | @since 2.01
    instance (Show a, Show b, Show c) => Show (a, b, c) where
      showsPrec _ (a,b,c) s = show_tuple [shows a, shows b, shows c] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d) => Show (a, b, c, d) where
      showsPrec _ (a,b,c,d) s = show_tuple [shows a, shows b, shows c, shows d] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e) => Show (a, b, c, d, e) where
      showsPrec _ (a,b,c,d,e) s = show_tuple [shows a, shows b, shows c, shows d, shows e] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f) => Show (a,b,c,d,e,f) where
      showsPrec _ (a,b,c,d,e,f) s = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g)
            => Show (a,b,c,d,e,f,g) where
      showsPrec _ (a,b,c,d,e,f,g) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h)
             => Show (a,b,c,d,e,f,g,h) where
      showsPrec _ (a,b,c,d,e,f,g,h) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i)
             => Show (a,b,c,d,e,f,g,h,i) where
      showsPrec _ (a,b,c,d,e,f,g,h,i) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j)
             => Show (a,b,c,d,e,f,g,h,i,j) where
      showsPrec _ (a,b,c,d,e,f,g,h,i,j) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i, shows j] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k)
             => Show (a,b,c,d,e,f,g,h,i,j,k) where
      showsPrec _ (a,b,c,d,e,f,g,h,i,j,k) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i, shows j, shows k] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k,
              Show l)
             => Show (a,b,c,d,e,f,g,h,i,j,k,l) where
      showsPrec _ (a,b,c,d,e,f,g,h,i,j,k,l) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i, shows j, shows k, shows l] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k,
              Show l, Show m)
             => Show (a,b,c,d,e,f,g,h,i,j,k,l,m) where
      showsPrec _ (a,b,c,d,e,f,g,h,i,j,k,l,m) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i, shows j, shows k, shows l, shows m] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k,
              Show l, Show m, Show n)
             => Show (a,b,c,d,e,f,g,h,i,j,k,l,m,n) where
      showsPrec _ (a,b,c,d,e,f,g,h,i,j,k,l,m,n) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i, shows j, shows k, shows l, shows m, shows n] s

    -- | @since 2.01
    instance (Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k,
              Show l, Show m, Show n, Show o)
             => Show (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o) where
      showsPrec _ (a,b,c,d,e,f,g,h,i,j,k,l,m,n,o) s
            = show_tuple [shows a, shows b, shows c, shows d, shows e, shows f, shows g, shows h,
                          shows i, shows j, shows k, shows l, shows m, shows n, shows o] s

    show_tuple :: [ShowS] -> ShowS
    show_tuple ss = showChar '('
                  . foldr1 (\s r -> s . showChar ',' . r) ss
                  . showChar ')'

    --------------------------------------------------------------
    -- Support code for Show
    --------------------------------------------------------------

    -- | equivalent to 'showsPrec' with a precedence of 0.
    shows           :: (Show a) => a -> ShowS
    shows           =  showsPrec 0

    -- | utility function converting a 'Char' to a show function that
    -- simply prepends the character unchanged.
    showChar        :: Char -> ShowS
    showChar        =  (:)

    -- | utility function converting a 'String' to a show function that
    -- simply prepends the string unchanged.
    showString      :: String -> ShowS
    showString      =  (++)

    -- | utility function that surrounds the inner show function with
    -- parentheses when the 'Bool' parameter is 'True'.
    showParen       :: Bool -> ShowS -> ShowS
    showParen b p   =  if b then showChar '(' . p . showChar ')' else p

    showSpace :: ShowS
    showSpace = {-showChar ' '-} \ xs -> ' ' : xs

    showCommaSpace :: ShowS
    showCommaSpace = showString ", "
    -- Code specific for characters

    -- | Convert a character to a string using only printable characters,
    -- using Haskell source-language escape conventions.  For example:
    --
    -- > showLitChar '\n' s  =  "\\n" ++ s
    --
    showLitChar                :: Char -> ShowS
    showLitChar c s | c > '\DEL' =  showChar '\\' (protectEsc isDec (shows (ord c)) s)
    showLitChar '\DEL'         s =  showString "\\DEL" s
    showLitChar '\\'           s =  showString "\\\\" s
    showLitChar c s | c >= ' '   =  showChar c s
    showLitChar '\a'           s =  showString "\\a" s
    showLitChar '\b'           s =  showString "\\b" s
    showLitChar '\f'           s =  showString "\\f" s
    showLitChar '\n'           s =  showString "\\n" s
    showLitChar '\r'           s =  showString "\\r" s
    showLitChar '\t'           s =  showString "\\t" s
    showLitChar '\v'           s =  showString "\\v" s
    showLitChar '\SO'          s =  protectEsc (== 'H') (showString "\\SO") s
    showLitChar c              s =  showString ('\\' : asciiTab!!ord c) s
            -- I've done manual eta-expansion here, because otherwise it's
            -- impossible to stop (asciiTab!!ord) getting floated out as an MFE

    showLitString :: String -> ShowS
    -- | Same as 'showLitChar', but for strings
    -- It converts the string to a string using Haskell escape conventions
    -- for non-printable characters. Does not add double-quotes around the
    -- whole thing; the caller should do that.
    -- The main difference from showLitChar (apart from the fact that the
    -- argument is a string not a list) is that we must escape double-quotes
    showLitString []         s = s
    showLitString ('"' : cs) s = showString "\\\"" (showLitString cs s)
    showLitString (c   : cs) s = showLitChar c (showLitString cs s)
       -- Making 's' an explicit parameter makes it clear to GHC that
       -- showLitString has arity 2, which avoids it allocating an extra lambda
       -- The sticking point is the recursive call to (showLitString cs), which
       -- it can't figure out would be ok with arity 2.

    showMultiLineString :: String -> [String]
    -- | Like 'showLitString' (expand escape characters using Haskell
    -- escape conventions), but
    --   * break the string into multiple lines
    --   * wrap the entire thing in double quotes
    -- Example:  @showMultiLineString "hello\ngoodbye\nblah"@
    -- returns   @["\"hello\\n\\", "\\goodbye\n\\", "\\blah\""]@
    showMultiLineString str
      = go '\"' str
      where
        go ch s = case break (== '\n') s of
                    (l, _:s'@(_:_)) -> (ch : showLitString l "\\n\\") : go '\\' s'
                    (l, "\n")       -> [ch : showLitString l "\\n\""]
                    (l, _)          -> [ch : showLitString l "\""]

    isDec :: Char -> Bool
    isDec c = c >= '0' && c <= '9'

    protectEsc :: (Char -> Bool) -> ShowS -> ShowS
    protectEsc p f             = f . cont
                                 where cont s@(c:_) | p c = "\\&" ++ s
                                       cont s             = s

    asciiTab :: [String]
    asciiTab = -- Using an array drags in the array module.  listArray ('\NUL', ' ')
               ["NUL", "SOH", "STX", "ETX", "EOT", "ENQ", "ACK", "BEL",
                "BS",  "HT",  "LF",  "VT",  "FF",  "CR",  "SO",  "SI",
                "DLE", "DC1", "DC2", "DC3", "DC4", "NAK", "SYN", "ETB",
                "CAN", "EM",  "SUB", "ESC", "FS",  "GS",  "RS",  "US",
                "SP"]

    -- Code specific for Ints.

    -- | Convert an 'Int' in the range @0@..@15@ to the corresponding single
    -- digit 'Char'.  This function fails on other inputs, and generates
    -- lower-case hexadecimal digits.
    intToDigit :: Int -> Char
    intToDigit (I# i)
        | isTrue# (i >=# 0#)  && isTrue# (i <=#  9#) = unsafeChr (ord '0' + I# i)
        | isTrue# (i >=# 10#) && isTrue# (i <=# 15#) = unsafeChr (ord 'a' + I# i - 10)
        | otherwise =  errorWithoutStackTrace ("Char.intToDigit: not a digit " ++ show (I# i))

    showSignedInt :: Int -> Int -> ShowS
    showSignedInt (I# p) (I# n) r
        | isTrue# (n <# 0#) && isTrue# (p ># 6#) = '(' : itos n (')' : r)
        | otherwise                              = itos n r

    itos :: Int# -> String -> String
    itos n# cs
        | isTrue# (n# <# 0#) =
            let !(I# minInt#) = minInt in
            if isTrue# (n# ==# minInt#)
                    -- negateInt# minInt overflows, so we can't do that:
               then '-' : (case n# `quotRemInt#` 10# of
                           (# q, r #) ->
                               itos' (negateInt# q) (itos' (negateInt# r) cs))
               else '-' : itos' (negateInt# n#) cs
        | otherwise = itos' n# cs
        where
        itos' :: Int# -> String -> String
        itos' x# cs'
            | isTrue# (x# <# 10#) = C# (chr# (ord# '0'# +# x#)) : cs'
            | otherwise = case x# `quotRemInt#` 10# of
                          (# q, r #) ->
                              case chr# (ord# '0'# +# r) of
                              c# ->
                                  itos' q (C# c# : cs')

    --------------------------------------------------------------
    -- The Integer instances for Show
    --------------------------------------------------------------

    -- | @since 2.01
    instance Show Integer where
        showsPrec p n r
            | p > 6 && n < 0 = '(' : integerToString n (')' : r)
            -- Minor point: testing p first gives better code
            -- in the not-uncommon case where the p argument
            -- is a constant
            | otherwise = integerToString n r
        showList = showList__ (showsPrec 0)

    -- Divide an conquer implementation of string conversion
    integerToString :: Integer -> String -> String
    integerToString n0 cs0
        | n0 < 0    = '-' : integerToString' (- n0) cs0
        | otherwise = integerToString' n0 cs0
        where
        integerToString' :: Integer -> String -> String
        integerToString' n cs
            | n < BASE  = jhead (fromInteger n) cs
            | otherwise = jprinth (jsplitf (BASE*BASE) n) cs

        -- Split n into digits in base p. We first split n into digits
        -- in base p*p and then split each of these digits into two.
        -- Note that the first 'digit' modulo p*p may have a leading zero
        -- in base p that we need to drop - this is what jsplith takes care of.
        -- jsplitb the handles the remaining digits.
        jsplitf :: Integer -> Integer -> [Integer]
        jsplitf p n
            | p > n     = [n]
            | otherwise = jsplith p (jsplitf (p*p) n)

        jsplith :: Integer -> [Integer] -> [Integer]
        jsplith p (n:ns) =
            case n `quotRemInteger` p of
            (# q, r #) ->
                if q > 0 then q : r : jsplitb p ns
                         else     r : jsplitb p ns
        jsplith _ [] = errorWithoutStackTrace "jsplith: []"

        jsplitb :: Integer -> [Integer] -> [Integer]
        jsplitb _ []     = []
        jsplitb p (n:ns) = case n `quotRemInteger` p of
                           (# q, r #) ->
                               q : r : jsplitb p ns

        -- Convert a number that has been split into digits in base BASE^2
        -- this includes a last splitting step and then conversion of digits
        -- that all fit into a machine word.
        jprinth :: [Integer] -> String -> String
        jprinth (n:ns) cs =
            case n `quotRemInteger` BASE of
            (# q', r' #) ->
                let q = fromInteger q'
                    r = fromInteger r'
                in if q > 0 then jhead q $ jblock r $ jprintb ns cs
                            else jhead r $ jprintb ns cs
        jprinth [] _ = errorWithoutStackTrace "jprinth []"

        jprintb :: [Integer] -> String -> String
        jprintb []     cs = cs
        jprintb (n:ns) cs = case n `quotRemInteger` BASE of
                            (# q', r' #) ->
                                let q = fromInteger q'
                                    r = fromInteger r'
                                in jblock q $ jblock r $ jprintb ns cs

        -- Convert an integer that fits into a machine word. Again, we have two
        -- functions, one that drops leading zeros (jhead) and one that doesn't
        -- (jblock)
        jhead :: Int -> String -> String
        jhead n cs
            | n < 10    = case unsafeChr (ord '0' + n) of
                c@(C# _) -> c : cs
            | otherwise = case unsafeChr (ord '0' + r) of
                c@(C# _) -> jhead q (c : cs)
            where
            (q, r) = n `quotRemInt` 10

        jblock = jblock' {- ' -} DIGITS

        jblock' :: Int -> Int -> String -> String
        jblock' d n cs
            | d == 1    = case unsafeChr (ord '0' + n) of
                 c@(C# _) -> c : cs
            | otherwise = case unsafeChr (ord '0' + r) of
                 c@(C# _) -> jblock' (d - 1) q (c : cs)
            where
            (q, r) = n `quotRemInt` 10