Portability	portable
Stability	provisional
Maintainer	libraries@haskell.org
Safe Haskell	Safe

Text.Show

Description

Converting values to readable strings: the Show class and associated functions.

Synopsis

Documentation

typeShowS = String -> String Source

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.

classShow a whereSource

Conversion of values to readable Strings.

Minimal complete definition: showsPrec or show.

Derived instances of Show have the following properties, which are compatible with derived instances of 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)".

Methods

showsPrec Source

Arguments

:: 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

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 Read and Show satisfy the following:

(x,"") is an element of (readsPrec d (showsPrec d x "")).

That is, readsPrec parses the string produced by showsPrec, and delivers the value that showsPrec started with.

show :: a -> String Source

A specialised variant of showsPrec, using precedence context zero, and returning an ordinary String.

showList :: [a] -> ShowS Source

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.

Instances

Show Bool
Show Char
Show Double
Show Float
Show Int
Show Int8
Show Int16
Show Int32
Show Int64
Show Integer
Show Ordering
Show Word
Show Word8
Show Word16
Show Word32
Show Word64
Show ()
Show TyCon
Show TypeRep
Show ArithException
Show ErrorCall
Show SomeException
Show IOException
Show MaskingState
Show Lexeme
Show IOMode
Show SeekMode
Show CUIntMax
Show CIntMax
Show CUIntPtr
Show CIntPtr
Show CSUSeconds
Show CUSeconds
Show CTime
Show CClock
Show CSigAtomic
Show CWchar
Show CSize
Show CPtrdiff
Show CDouble
Show CFloat
Show CULLong
Show CLLong
Show CULong
Show CLong
Show CUInt
Show CInt
Show CUShort
Show CShort
Show CUChar
Show CSChar
Show CChar
Show GeneralCategory
Show Associativity
Show Fixity
Show Arity
Show Dynamic
Show IntPtr
Show WordPtr
Show Any
Show All
Show CodingProgress
Show TextEncoding
Show NewlineMode
Show Newline
Show BufferMode
Show Handle
Show IOErrorType
Show ExitCode
Show ArrayException
Show AsyncException
Show AssertionFailed
Show Deadlock
Show BlockedIndefinitelyOnSTM
Show BlockedIndefinitelyOnMVar
Show CodingFailureMode
Show ThreadStatus
Show BlockReason
Show ThreadId
Show NestedAtomically
Show NonTermination
Show NoMethodError
Show RecUpdError
Show RecConError
Show RecSelError
Show PatternMatchFail
Show Fd
Show CRLim
Show CTcflag
Show CSpeed
Show CCc
Show CUid
Show CNlink
Show CGid
Show CSsize
Show CPid
Show COff
Show CMode
Show CIno
Show CDev
Show Event
Show FdKey
Show HandlePosn
Show Fixity
Show ConstrRep
Show DataRep
Show Constr
Show DataType
Show GCStats
Show Version
Show a => Show [a]
(Integral a, Show a) => Show (Ratio a)
Show (Ptr a)
Show (FunPtr a)
Show a => Show (Maybe a)
Show (ForeignPtr a)
Show (IsEven n)
Show (IsZero n)
Show a => Show (Last a)
Show a => Show (First a)
Show a => Show (Product a)
Show a => Show (Sum a)
Show a => Show (Dual a)
Show a => Show (Complex a)
HasResolution a => Show (Fixed a)
Show (a -> b)
(Show a, Show b) => Show (Either a b)
(Show a, Show b) => Show (a, b)
Show (ST s a)
(SingE k (Kind k) rep, Show rep) => Show (Sing k a)
(Show a, Show b, Show c) => Show (a, b, c)
(Show a, Show b, Show c, Show d) => Show (a, b, c, d)
(Show a, Show b, Show c, Show d, Show e) => Show (a, b, c, d, e)
(Show a, Show b, Show c, Show d, Show e, Show f) => Show (a, b, c, d, e, f)
(Show a, Show b, Show c, Show d, Show e, Show f, Show g) => Show (a, b, c, d, e, f, g)
(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)
(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)
(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)
(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)
(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)
(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)
(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)
(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)

shows :: Show a => a -> ShowS Source

equivalent to showsPrec with a precedence of 0.

showChar :: Char -> ShowS Source

utility function converting a Char to a show function that simply prepends the character unchanged.

showString :: String -> ShowS Source

utility function converting a String to a show function that simply prepends the string unchanged.

showParen :: Bool -> ShowS -> ShowS Source

utility function that surrounds the inner show function with parentheses when the Bool parameter is True.

showListWith :: (a -> ShowS) -> [a] -> ShowS Source

Show a list (using square brackets and commas), given a function for showing elements.