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 | :: 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 -> String | A specialised variant of showsPrec, using precedence context
zero, and returning an ordinary String. | | showList :: [a] -> ShowS | 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 | (Ix ix, Show ix, Show e, IArray UArray e) => Show (UArray ix e) | (Ix ix, Show ix, Show e) => Show (DiffArray ix e) | (Ix ix, Show ix) => Show (DiffUArray ix Char) | (Ix ix, Show ix) => Show (DiffUArray ix Int) | (Ix ix, Show ix) => Show (DiffUArray ix Word) | (Ix ix, Show ix) => Show (DiffUArray ix Float) | (Ix ix, Show ix) => Show (DiffUArray ix Double) | (Ix ix, Show ix) => Show (DiffUArray ix Int8) | (Ix ix, Show ix) => Show (DiffUArray ix Int16) | (Ix ix, Show ix) => Show (DiffUArray ix Int32) | (Ix ix, Show ix) => Show (DiffUArray ix Int64) | (Ix ix, Show ix) => Show (DiffUArray ix Word8) | (Ix ix, Show ix) => Show (DiffUArray ix Word16) | (Ix ix, Show ix) => Show (DiffUArray ix Word32) | (Ix ix, Show ix) => Show (DiffUArray ix Word64) | Show GeneralCategory | (RealFloat a, Show a) => Show (Complex a) | Show Dynamic | HasResolution a => Show (Fixed a) | Show Constr | Show DataType | Show DataRep | Show ConstrRep | Show Fixity | Show HashData | Show a => Show (IntMap a) | Show IntSet | (Show k, Show a) => Show (Map k a) | Show All | Show Any | Show a => Show (Sum a) | Show a => Show (Product a) | Show PackedString | Show a => Show (Seq a) | Show a => Show (ViewL a) | Show a => Show (ViewR a) | Show a => Show (Set a) | Show a => Show (Tree a) | Show TypeRep | Show TyCon | Show Version | Show CChar | Show CSChar | Show CUChar | Show CShort | Show CUShort | Show CInt | Show CUInt | Show CLong | Show CULong | Show CLLong | Show CULLong | Show CFloat | Show CDouble | Show CLDouble | Show CPtrdiff | Show CSize | Show CWchar | Show CSigAtomic | Show CClock | Show CTime | Show CIntPtr | Show CUIntPtr | Show CIntMax | Show CUIntMax | Show WordPtr | Show IntPtr | (Ix a, Show a, Show b) => Show (Array a b) | Show ThreadId | Show Float | Show Double | Show (ForeignPtr a) | Show (Ptr a) | Show (FunPtr a) | Show HandlePosn | Show SeekMode | Show HandleType | Show Handle | Show ArithException | Show AsyncException | Show ArrayException | Show Exception | Show IOErrorType | Show IOException | Show BufferMode | Show ExitCode | Show IOMode | Show Int8 | Show Int16 | Show Int32 | Show Int64 | Show Integer | Integral a => Show (Ratio a) | Show (ST s a) | Show () | Show a => Show [a] | Show Bool | Show Ordering | Show Char | Show Int | Show a => Show (Maybe a) | (Show a, Show b) => Show (Either a b) | (Show a, Show b) => Show (a, b) | (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) | Show Word | Show Word8 | Show Word16 | Show Word32 | Show Word64 | Show Permissions | Show TimeLocale | Show CDev | Show CIno | Show CMode | Show COff | Show CPid | Show CSsize | Show CGid | Show CNlink | Show CUid | Show CCc | Show CSpeed | Show CTcflag | Show CRLim | Show Fd | Show StdGen | Show ClockTime | Show Month | Show Day | Show CalendarTime | Show TimeDiff | Show Doc | Show Lexeme | Show (a -> b) |
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