base-4.6.0.0: Basic libraries

Portabilityportable
Stabilityprovisional
Maintainerlibraries@haskell.org
Safe HaskellSafe

Text.Show

Description

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

Synopsis

Documentation

type ShowS = String -> StringSource

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.

class Show 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

showsPrecSource

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:

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

show :: a -> StringSource

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

showList :: [a] -> ShowSSource

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 ConsoleEvent 
Show Fd 
Show CSsize 
Show CPid 
Show COff 
Show CMode 
Show CIno 
Show CDev 
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 (IsEven n) 
Show (IsZero n) 
Show (ForeignPtr a) 
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 -> ShowSSource

equivalent to showsPrec with a precedence of 0.

showChar :: Char -> ShowSSource

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

showString :: String -> ShowSSource

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

showParen :: Bool -> ShowS -> ShowSSource

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

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

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