Copyright | (c) The University of Glasgow 2001 |
---|---|
License | BSD-style (see the file libraries/base/LICENSE) |
Maintainer | libraries@haskell.org |
Stability | provisional |
Portability | portable |
Safe Haskell | Safe |
Language | Haskell2010 |
Text.Show
Description
Converting values to readable strings:
the Show
class and associated functions.
Documentation
Conversion of values to readable String
s.
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 thand
(associativity is ignored). Thus, ifd
is0
then the result is never surrounded in parentheses; ifd
is11
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,
produces the stringshow
(Leaf 1 :^: Leaf 2 :^: Leaf 3)"Leaf 1 :^: (Leaf 2 :^: Leaf 3)"
.
Methods
Arguments
the operator precedence of the enclosing
context (a number from 0
to 11
).
Function application has precedence 10
.
the value to be converted to a String
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.
Instances
Instances details
Instance details
Defined in Data.Typeable.Internal
Instance details
Defined in GHC.Exception.Type
Instance details
Defined in GHC.Unicode
Instance details
Defined in GHC.Fingerprint.Type
Instance details
Defined in Foreign.C.Types
Instance details
Defined in Foreign.C.Types
Instance details
Defined in GHC.TypeLits
Instance details
Defined in GHC.Generics
Instance details
Defined in GHC.Generics
Instance details
Defined in GHC.Generics
Instance details
Defined in GHC.Generics
Instance details
Defined in GHC.Exception.Type
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Encoding.Types
Instance details
Defined in GHC.IO.Encoding.Types
Instance details
Defined in GHC.IO.Handle.Types
Instance details
Defined in GHC.IO.Handle.Types
Instance details
Defined in GHC.IO.Handle.Types
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Exception
Instance details
Defined in GHC.IO.Encoding.Failure
Instance details
Defined in GHC.Conc.Sync
Instance details
Defined in GHC.Conc.Sync
Instance details
Defined in Control.Exception.Base
Instance details
Defined in Control.Exception.Base
Instance details
Defined in Control.Exception.Base
Instance details
Defined in Control.Exception.Base
Instance details
Defined in Control.Exception.Base
Instance details
Defined in Control.Exception.Base
Instance details
Defined in Control.Exception.Base
Instance details
Defined in GHC.IO.Handle.Lock
Instance details
Defined in GHC.IO.Handle
Instance details
Defined in GHC.StaticPtr
Instance details
Defined in GHC.RTS.Flags
Instance details
Defined in GHC.RTS.Flags
Instance details
Defined in GHC.RTS.Flags
Instance details
Defined in GHC.RTS.Flags
Instance details
Defined in GHC.RTS.Flags
Instance details
Defined in GHC.RTS.Flags
Instance details
Defined in GHC.ForeignPtr
This instance would be equivalent to the derived instances of the
Identity
newtype if the runIdentity
field were removed
Since: 4.8.0.0
Instance details
Defined in Data.Semigroup
This instance would be equivalent to the derived instances of the
Const
newtype if the getConst
field were removed
Since: 4.8.0.0
Since: 2.1
Since: 2.1
Since: 2.1
Since: 2.1
Since: 2.1
Since: 2.1
Since: 2.1
Since: 2.1
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.
showListWith :: (a -> ShowS) -> [a] -> ShowS Source #
Show a list (using square brackets and commas), given a function for showing elements.