Copyright | (c) The University of Glasgow 2001 |
---|---|
License | BSD-style (see the file libraries/base/LICENSE) |
Maintainer | [email protected] |
Stability | provisional |
Portability | portable |
Safe Haskell | Safe |
Language | Haskell2010 |
Converting values to readable strings: the Show
class and associated functions.
type ShowS = 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.
Conversion of values to readable String
s.
Derived instances of Show
have the following properties, which are compatible with derived instances of Read
:
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.showsPrec
will produce infix applications of the constructor.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.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)"
.:: Int | the operator precedence of the enclosing context (a number from |
-> a | the value to be converted to a |
-> 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.
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.
Show Bool | |
Show Char | Since: 2.1 |
Show Int | Since: 2.1 |
Show Int8 | Since: 2.1 |
Show Int16 | Since: 2.1 |
Show Int32 | Since: 2.1 |
Show Int64 | Since: 2.1 |
Show Integer | Since: 2.1 |
Show Natural | Since: 4.8.0.0 |
Show Ordering | |
Show Word | Since: 2.1 |
Show Word8 | Since: 2.1 |
Show Word16 | Since: 2.1 |
Show Word32 | Since: 2.1 |
Show Word64 | Since: 2.1 |
Show CallStack | Since: 4.9.0.0 |
Show SomeTypeRep | Since: 4.10.0.0 |
Show () | |
Show TyCon | Since: 2.1 |
Show Module | Since: 4.9.0.0 |
Show TrName | Since: 4.9.0.0 |
Show SrcLoc | |
Show SomeException | Since: 3.0 |
Show GeneralCategory | |
Show Number | |
Show Lexeme | |
Show Fingerprint | Since: 4.7.0.0 |
Show IOMode | |
Show IntPtr | |
Show WordPtr | |
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 CBool | |
Show CULLong | |
Show CLLong | |
Show CULong | |
Show CLong | |
Show CUInt | |
Show CInt | |
Show CUShort | |
Show CShort | |
Show CUChar | |
Show CSChar | |
Show CChar | |
Show SomeNat | Since: 4.7.0.0 |
Show SomeSymbol | Since: 4.7.0.0 |
Show DecidedStrictness | |
Show SourceStrictness | |
Show SourceUnpackedness | |
Show Associativity | |
Show Fixity | |
Show Any | |
Show All | |
Show ArithException | Since: 4.0.0.0 |
Show ErrorCall | Since: 4.0.0.0 |
Show IOException | Since: 4.1.0.0 |
Show MaskingState | |
Show CodingProgress | |
Show TextEncoding | Since: 4.3.0.0 |
Show SeekMode | |
Show NewlineMode | |
Show Newline | |
Show BufferMode | |
Show Handle | Since: 4.1.0.0 |
Show IOErrorType | Since: 4.1.0.0 |
Show ExitCode | |
Show ArrayException | Since: 4.1.0.0 |
Show AsyncException | Since: 4.1.0.0 |
Show SomeAsyncException | Since: 4.7.0.0 |
Show AssertionFailed | Since: 4.1.0.0 |
Show CompactionFailed | Since: 4.10.0.0 |
Show AllocationLimitExceeded | Since: 4.7.1.0 |
Show Deadlock | Since: 4.1.0.0 |
Show BlockedIndefinitelyOnSTM | Since: 4.1.0.0 |
Show BlockedIndefinitelyOnMVar | Since: 4.1.0.0 |
Show CodingFailureMode | |
Show Fd | |
Show CTimer | |
Show CKey | |
Show CId | |
Show CFsFilCnt | |
Show CFsBlkCnt | |
Show CClockId | |
Show CBlkCnt | |
Show CBlkSize | |
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 Lifetime | |
Show Event | Since: 4.3.1.0 |
Show Dynamic | Since: 2.1 |
Show ThreadStatus | |
Show BlockReason | |
Show ThreadId | Since: 4.2.0.0 |
Show NestedAtomically | Since: 4.0 |
Show NonTermination | Since: 4.0 |
Show TypeError | Since: 4.9.0.0 |
Show NoMethodError | Since: 4.0 |
Show RecUpdError | Since: 4.0 |
Show RecConError | Since: 4.0 |
Show RecSelError | Since: 4.0 |
Show PatternMatchFail | Since: 4.0 |
Show FdKey | |
Show FileLockingNotSupported | |
Show HandlePosn | Since: 4.1.0.0 |
Show Version | |
Show GCStats | |
Show GCDetails | |
Show RTSStats | |
Show RTSFlags | |
Show ParFlags | |
Show TickyFlags | |
Show TraceFlags | |
Show DoTrace | |
Show ProfFlags | |
Show DoHeapProfile | |
Show CCFlags | |
Show DoCostCentres | |
Show DebugFlags | |
Show MiscFlags | |
Show ConcFlags | |
Show GCFlags | |
Show GiveGCStats | |
Show Fixity | |
Show ConstrRep | |
Show DataRep | |
Show Constr | Since: 4.0.0.0 |
Show DataType | |
Show StaticPtrInfo | |
Show Void | Since: 4.8.0.0 |
Show a => Show [a] | Since: 2.1 |
Show a => Show (Maybe a) | |
Show a => Show (Ratio a) | Since: 2.0.1 |
Show (Ptr a) | Since: 2.1 |
Show (FunPtr a) | Since: 2.1 |
Show p => Show (Par1 p) | |
Show a => Show (Down 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 (ForeignPtr a) | Since: 2.1 |
Show a => Show (Identity a) |
This instance would be equivalent to the derived instances of the Since: 4.8.0.0 |
Show a => Show (ZipList a) | |
Show a => Show (NonEmpty a) | |
Show a => Show (Option a) | |
Show m => Show (WrappedMonoid m) | |
Show a => Show (Last a) | |
Show a => Show (First a) | |
Show a => Show (Max a) | |
Show a => Show (Min a) | |
HasResolution a => Show (Fixed a) | Since: 2.1 |
Show a => Show (Complex a) | |
(Show b, Show a) => Show (Either a b) | |
Show (V1 k p) | |
Show (U1 k p) | Since: 4.9.0.0 |
Show (TypeRep k a) | |
(Show a, Show b) => Show (a, b) | Since: 2.1 |
Show (ST s a) | Since: 2.1 |
Show (Proxy k s) | Since: 4.7.0.0 |
(Show b, Show a) => Show (Arg a b) | |
Show (f p) => Show (Rec1 k f p) | |
Show (URec k Word p) | |
Show (URec k Int p) | |
Show (URec k Float p) | |
Show (URec k Double p) | |
Show (URec k Char p) | |
(Show a, Show b, Show c) => Show (a, b, c) | Since: 2.1 |
Show ((:~:) k a b) | |
Show (Coercion k a b) | |
Show (f a) => Show (Alt k f a) | |
Show a => Show (Const k a b) |
This instance would be equivalent to the derived instances of the Since: 4.8.0.0 |
Show c => Show (K1 k i c p) | |
(Show (g p), Show (f p)) => Show ((:+:) k f g p) | |
(Show (g p), Show (f p)) => Show ((:*:) k f g p) | |
(Show a, Show b, Show c, Show d) => Show (a, b, c, d) | Since: 2.1 |
Show ((:~~:) k1 k2 a b) | Since: 4.10.0.0 |
(Show1 f, Show1 g, Show a) => Show (Sum * f g a) | Since: 4.9.0.0 |
(Show1 f, Show1 g, Show a) => Show (Product * f g a) | Since: 4.9.0.0 |
Show (f p) => Show (M1 k i c f p) | |
Show (f (g p)) => Show ((:.:) k2 k1 f g p) | |
(Show a, Show b, Show c, Show d, Show e) => Show (a, b, c, d, e) | Since: 2.1 |
(Show1 f, Show1 g, Show a) => Show (Compose * * f g a) | Since: 4.9.0.0 |
(Show a, Show b, Show c, Show d, Show e, Show f) => Show (a, b, c, d, e, f) | Since: 2.1 |
(Show a, Show b, Show c, Show d, Show e, Show f, Show g) => Show (a, b, c, d, e, f, g) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
(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) | Since: 2.1 |
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.
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.2.1/docs/html/libraries/base-4.10.0.0/Text-Show.html