GHC.Read

The Read class and instances for basic data types.

Class

class Read a where

Parsing of Strings, producing values.

Derived instances of Read make the following assumptions, which derived instances of Show obey:

• If the constructor is defined to be an infix operator, then the derived Read instance will parse only infix applications of the constructor (not the prefix form).
• Associativity is not used to reduce the occurrence of parentheses, although precedence may be.
• If the constructor is defined using record syntax, the derived Read will parse only the record-syntax form, and furthermore, the fields must be given in the same order as the original declaration.
• The derived Read instance allows arbitrary Haskell whitespace between tokens of the input string. Extra parentheses are also allowed.

For example, given the declarations

infixr 5 :^:
data Tree a =  Leaf a  |  Tree a :^: Tree a

the derived instance of Read in Haskell 2010 is equivalent to

instance (Read a) => Read (Tree a) where

        readsPrec d r =  readParen (d > app_prec)
                         (\r -> [(Leaf m,t) |
                                 ("Leaf",s) <- lex r,
                                 (m,t) <- readsPrec (app_prec+1) s]) r

                      ++ readParen (d > up_prec)
                         (\r -> [(u:^:v,w) |
                                 (u,s) <- readsPrec (up_prec+1) r,
                                 (":^:",t) <- lex s,
                                 (v,w) <- readsPrec (up_prec+1) t]) r

          where app_prec = 10
                up_prec = 5

Note that right-associativity of :^: is unused.

The derived instance in GHC is equivalent to

instance (Read a) => Read (Tree a) where

        readPrec = parens $ (prec app_prec $ do
                                 Ident "Leaf" <- lexP
                                 m <- step readPrec
                                 return (Leaf m))

                     +++ (prec up_prec $ do
                                 u <- step readPrec
                                 Symbol ":^:" <- lexP
                                 v <- step readPrec
                                 return (u :^: v))

          where app_prec = 10
                up_prec = 5

        readListPrec = readListPrecDefault

Why do both readsPrec and readPrec exist, and why does GHC opt to implement readPrec in derived Read instances instead of readsPrec? The reason is that readsPrec is based on the ReadS type, and although ReadS is mentioned in the Haskell 2010 Report, it is not a very efficient parser data structure.

readPrec, on the other hand, is based on a much more efficient ReadPrec datatype (a.k.a "new-style parsers"), but its definition relies on the use of the RankNTypes language extension. Therefore, readPrec (and its cousin, readListPrec) are marked as GHC-only. Nevertheless, it is recommended to use readPrec instead of readsPrec whenever possible for the efficiency improvements it brings.

As mentioned above, derived Read instances in GHC will implement readPrec instead of readsPrec. The default implementations of readsPrec (and its cousin, readList) will simply use readPrec under the hood. If you are writing a Read instance by hand, it is recommended to write it like so:

instance Read T where
  readPrec     = ...
  readListPrec = readListPrecDefault

Minimal complete definition

readsPrec | readPrec

Methods

readsPrec

Arguments

:: Int

the operator precedence of the enclosing context (a number from 0 to 11). Function application has precedence 10.

-> ReadS a

attempts to parse a value from the front of the string, returning a list of (parsed value, remaining string) pairs. If there is no successful parse, the returned list is empty.

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.

readList :: ReadS [a]

The method readList is provided to allow the programmer to give a specialised way of parsing lists of values. For example, this is used by the predefined Read instance of the Char type, where values of type String are expected to use double quotes, rather than square brackets.

readPrec :: ReadPrec a

Proposed replacement for readsPrec using new-style parsers (GHC only).

readListPrec :: ReadPrec [a]

Proposed replacement for readList using new-style parsers (GHC only). The default definition uses readList. Instances that define readPrec should also define readListPrec as readListPrecDefault.

Instances

Read Void

Reading a Void value is always a parse error, considering Void as a data type with no constructors.

Since: base-4.8.0.0

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Void

readList :: ReadS [Void]

readPrec :: ReadPrec Void

readListPrec :: ReadPrec [Void]

Read ByteOrder

Since: base-4.11.0.0

Defined in GHC.Internal.ByteOrder

Methods

readsPrec :: Int -> ReadS ByteOrder

readList :: ReadS [ByteOrder]

readPrec :: ReadPrec ByteOrder

readListPrec :: ReadPrec [ByteOrder]

Read All

Since: base-2.1

Defined in GHC.Internal.Data.Semigroup.Internal

Methods

readsPrec :: Int -> ReadS All

readList :: ReadS [All]

readPrec :: ReadPrec All

readListPrec :: ReadPrec [All]

Read Any

Since: base-2.1

Defined in GHC.Internal.Data.Semigroup.Internal

Methods

readsPrec :: Int -> ReadS Any

readList :: ReadS [Any]

readPrec :: ReadPrec Any

readListPrec :: ReadPrec [Any]

Read Version

Since: base-2.1

Defined in GHC.Internal.Data.Version

Methods

readsPrec :: Int -> ReadS Version

readList :: ReadS [Version]

readPrec :: ReadPrec Version

readListPrec :: ReadPrec [Version]

Read CBool

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CBool

readList :: ReadS [CBool]

readPrec :: ReadPrec CBool

readListPrec :: ReadPrec [CBool]

Read CChar

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CChar

readList :: ReadS [CChar]

readPrec :: ReadPrec CChar

readListPrec :: ReadPrec [CChar]

Read CClock

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CClock

readList :: ReadS [CClock]

readPrec :: ReadPrec CClock

readListPrec :: ReadPrec [CClock]

Read CDouble

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CDouble

readList :: ReadS [CDouble]

readPrec :: ReadPrec CDouble

readListPrec :: ReadPrec [CDouble]

Read CFloat

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CFloat

readList :: ReadS [CFloat]

readPrec :: ReadPrec CFloat

readListPrec :: ReadPrec [CFloat]

Read CInt

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CInt

readList :: ReadS [CInt]

readPrec :: ReadPrec CInt

readListPrec :: ReadPrec [CInt]

Read CIntMax

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CIntMax

readList :: ReadS [CIntMax]

readPrec :: ReadPrec CIntMax

readListPrec :: ReadPrec [CIntMax]

Read CIntPtr

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CIntPtr

readList :: ReadS [CIntPtr]

readPrec :: ReadPrec CIntPtr

readListPrec :: ReadPrec [CIntPtr]

Read CLLong

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CLLong

readList :: ReadS [CLLong]

readPrec :: ReadPrec CLLong

readListPrec :: ReadPrec [CLLong]

Read CLong

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CLong

readList :: ReadS [CLong]

readPrec :: ReadPrec CLong

readListPrec :: ReadPrec [CLong]

Read CPtrdiff

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CPtrdiff

readList :: ReadS [CPtrdiff]

readPrec :: ReadPrec CPtrdiff

readListPrec :: ReadPrec [CPtrdiff]

Read CSChar

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CSChar

readList :: ReadS [CSChar]

readPrec :: ReadPrec CSChar

readListPrec :: ReadPrec [CSChar]

Read CSUSeconds

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CSUSeconds

readList :: ReadS [CSUSeconds]

readPrec :: ReadPrec CSUSeconds

readListPrec :: ReadPrec [CSUSeconds]

Read CShort

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CShort

readList :: ReadS [CShort]

readPrec :: ReadPrec CShort

readListPrec :: ReadPrec [CShort]

Read CSigAtomic

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CSigAtomic

readList :: ReadS [CSigAtomic]

readPrec :: ReadPrec CSigAtomic

readListPrec :: ReadPrec [CSigAtomic]

Read CSize

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CSize

readList :: ReadS [CSize]

readPrec :: ReadPrec CSize

readListPrec :: ReadPrec [CSize]

Read CTime

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CTime

readList :: ReadS [CTime]

readPrec :: ReadPrec CTime

readListPrec :: ReadPrec [CTime]

Read CUChar

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CUChar

readList :: ReadS [CUChar]

readPrec :: ReadPrec CUChar

readListPrec :: ReadPrec [CUChar]

Read CUInt

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CUInt

readList :: ReadS [CUInt]

readPrec :: ReadPrec CUInt

readListPrec :: ReadPrec [CUInt]

Read CUIntMax

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CUIntMax

readList :: ReadS [CUIntMax]

readPrec :: ReadPrec CUIntMax

readListPrec :: ReadPrec [CUIntMax]

Read CUIntPtr

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CUIntPtr

readList :: ReadS [CUIntPtr]

readPrec :: ReadPrec CUIntPtr

readListPrec :: ReadPrec [CUIntPtr]

Read CULLong

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CULLong

readList :: ReadS [CULLong]

readPrec :: ReadPrec CULLong

readListPrec :: ReadPrec [CULLong]

Read CULong

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CULong

readList :: ReadS [CULong]

readPrec :: ReadPrec CULong

readListPrec :: ReadPrec [CULong]

Read CUSeconds

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CUSeconds

readList :: ReadS [CUSeconds]

readPrec :: ReadPrec CUSeconds

readListPrec :: ReadPrec [CUSeconds]

Read CUShort

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CUShort

readList :: ReadS [CUShort]

readPrec :: ReadPrec CUShort

readListPrec :: ReadPrec [CUShort]

Read CWchar

Defined in GHC.Internal.Foreign.C.Types

Methods

readsPrec :: Int -> ReadS CWchar

readList :: ReadS [CWchar]

readPrec :: ReadPrec CWchar

readListPrec :: ReadPrec [CWchar]

Read IntPtr

Defined in GHC.Internal.Foreign.Ptr

Methods

readsPrec :: Int -> ReadS IntPtr

readList :: ReadS [IntPtr]

readPrec :: ReadPrec IntPtr

readListPrec :: ReadPrec [IntPtr]

Read WordPtr

Defined in GHC.Internal.Foreign.Ptr

Methods

readsPrec :: Int -> ReadS WordPtr

readList :: ReadS [WordPtr]

readPrec :: ReadPrec WordPtr

readListPrec :: ReadPrec [WordPtr]

Read Associativity

Since: base-4.6.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS Associativity

readList :: ReadS [Associativity]

readPrec :: ReadPrec Associativity

readListPrec :: ReadPrec [Associativity]

Read DecidedStrictness

Since: base-4.9.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS DecidedStrictness

readList :: ReadS [DecidedStrictness]

readPrec :: ReadPrec DecidedStrictness

readListPrec :: ReadPrec [DecidedStrictness]

Read Fixity

Since: base-4.6.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS Fixity

readList :: ReadS [Fixity]

readPrec :: ReadPrec Fixity

readListPrec :: ReadPrec [Fixity]

Read SourceStrictness

Since: base-4.9.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS SourceStrictness

readList :: ReadS [SourceStrictness]

readPrec :: ReadPrec SourceStrictness

readListPrec :: ReadPrec [SourceStrictness]

Read SourceUnpackedness

Since: base-4.9.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS SourceUnpackedness

readList :: ReadS [SourceUnpackedness]

readPrec :: ReadPrec SourceUnpackedness

readListPrec :: ReadPrec [SourceUnpackedness]

Read SeekMode

Since: base-4.2.0.0

Defined in GHC.Internal.IO.Device

Methods

readsPrec :: Int -> ReadS SeekMode

readList :: ReadS [SeekMode]

readPrec :: ReadPrec SeekMode

readListPrec :: ReadPrec [SeekMode]

Read ExitCode

Defined in GHC.Internal.IO.Exception

Methods

readsPrec :: Int -> ReadS ExitCode

readList :: ReadS [ExitCode]

readPrec :: ReadPrec ExitCode

readListPrec :: ReadPrec [ExitCode]

Read BufferMode

Since: base-4.2.0.0

Defined in GHC.Internal.IO.Handle.Types

Methods

readsPrec :: Int -> ReadS BufferMode

readList :: ReadS [BufferMode]

readPrec :: ReadPrec BufferMode

readListPrec :: ReadPrec [BufferMode]

Read Newline

Since: base-4.3.0.0

Defined in GHC.Internal.IO.Handle.Types

Methods

readsPrec :: Int -> ReadS Newline

readList :: ReadS [Newline]

readPrec :: ReadPrec Newline

readListPrec :: ReadPrec [Newline]

Read NewlineMode

Since: base-4.3.0.0

Defined in GHC.Internal.IO.Handle.Types

Methods

readsPrec :: Int -> ReadS NewlineMode

readList :: ReadS [NewlineMode]

readPrec :: ReadPrec NewlineMode

readListPrec :: ReadPrec [NewlineMode]

Read IOMode

Since: base-4.2.0.0

Defined in GHC.Internal.IO.IOMode

Methods

readsPrec :: Int -> ReadS IOMode

readList :: ReadS [IOMode]

readPrec :: ReadPrec IOMode

readListPrec :: ReadPrec [IOMode]

Read Int16

Since: base-2.1

Defined in GHC.Internal.Int

Methods

readsPrec :: Int -> ReadS Int16

readList :: ReadS [Int16]

readPrec :: ReadPrec Int16

readListPrec :: ReadPrec [Int16]

Read Int32

Since: base-2.1

Defined in GHC.Internal.Int

Methods

readsPrec :: Int -> ReadS Int32

readList :: ReadS [Int32]

readPrec :: ReadPrec Int32

readListPrec :: ReadPrec [Int32]

Read Int64

Since: base-2.1

Defined in GHC.Internal.Int

Methods

readsPrec :: Int -> ReadS Int64

readList :: ReadS [Int64]

readPrec :: ReadPrec Int64

readListPrec :: ReadPrec [Int64]

Read Int8

Since: base-2.1

Defined in GHC.Internal.Int

Methods

readsPrec :: Int -> ReadS Int8

readList :: ReadS [Int8]

readPrec :: ReadPrec Int8

readListPrec :: ReadPrec [Int8]

Read GCDetails

Since: base-4.10.0.0

Defined in GHC.Internal.Stats

Methods

readsPrec :: Int -> ReadS GCDetails

readList :: ReadS [GCDetails]

readPrec :: ReadPrec GCDetails

readListPrec :: ReadPrec [GCDetails]

Read RTSStats

Since: base-4.10.0.0

Defined in GHC.Internal.Stats

Methods

readsPrec :: Int -> ReadS RTSStats

readList :: ReadS [RTSStats]

readPrec :: ReadPrec RTSStats

readListPrec :: ReadPrec [RTSStats]

Read CBlkCnt

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CBlkCnt

readList :: ReadS [CBlkCnt]

readPrec :: ReadPrec CBlkCnt

readListPrec :: ReadPrec [CBlkCnt]

Read CBlkSize

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CBlkSize

readList :: ReadS [CBlkSize]

readPrec :: ReadPrec CBlkSize

readListPrec :: ReadPrec [CBlkSize]

Read CCc

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CCc

readList :: ReadS [CCc]

readPrec :: ReadPrec CCc

readListPrec :: ReadPrec [CCc]

Read CClockId

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CClockId

readList :: ReadS [CClockId]

readPrec :: ReadPrec CClockId

readListPrec :: ReadPrec [CClockId]

Read CDev

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CDev

readList :: ReadS [CDev]

readPrec :: ReadPrec CDev

readListPrec :: ReadPrec [CDev]

Read CFsBlkCnt

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CFsBlkCnt

readList :: ReadS [CFsBlkCnt]

readPrec :: ReadPrec CFsBlkCnt

readListPrec :: ReadPrec [CFsBlkCnt]

Read CFsFilCnt

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CFsFilCnt

readList :: ReadS [CFsFilCnt]

readPrec :: ReadPrec CFsFilCnt

readListPrec :: ReadPrec [CFsFilCnt]

Read CGid

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CGid

readList :: ReadS [CGid]

readPrec :: ReadPrec CGid

readListPrec :: ReadPrec [CGid]

Read CId

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CId

readList :: ReadS [CId]

readPrec :: ReadPrec CId

readListPrec :: ReadPrec [CId]

Read CIno

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CIno

readList :: ReadS [CIno]

readPrec :: ReadPrec CIno

readListPrec :: ReadPrec [CIno]

Read CKey

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CKey

readList :: ReadS [CKey]

readPrec :: ReadPrec CKey

readListPrec :: ReadPrec [CKey]

Read CMode

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CMode

readList :: ReadS [CMode]

readPrec :: ReadPrec CMode

readListPrec :: ReadPrec [CMode]

Read CNfds

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CNfds

readList :: ReadS [CNfds]

readPrec :: ReadPrec CNfds

readListPrec :: ReadPrec [CNfds]

Read CNlink

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CNlink

readList :: ReadS [CNlink]

readPrec :: ReadPrec CNlink

readListPrec :: ReadPrec [CNlink]

Read COff

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS COff

readList :: ReadS [COff]

readPrec :: ReadPrec COff

readListPrec :: ReadPrec [COff]

Read CPid

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CPid

readList :: ReadS [CPid]

readPrec :: ReadPrec CPid

readListPrec :: ReadPrec [CPid]

Read CRLim

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CRLim

readList :: ReadS [CRLim]

readPrec :: ReadPrec CRLim

readListPrec :: ReadPrec [CRLim]

Read CSocklen

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CSocklen

readList :: ReadS [CSocklen]

readPrec :: ReadPrec CSocklen

readListPrec :: ReadPrec [CSocklen]

Read CSpeed

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CSpeed

readList :: ReadS [CSpeed]

readPrec :: ReadPrec CSpeed

readListPrec :: ReadPrec [CSpeed]

Read CSsize

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CSsize

readList :: ReadS [CSsize]

readPrec :: ReadPrec CSsize

readListPrec :: ReadPrec [CSsize]

Read CTcflag

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CTcflag

readList :: ReadS [CTcflag]

readPrec :: ReadPrec CTcflag

readListPrec :: ReadPrec [CTcflag]

Read CUid

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS CUid

readList :: ReadS [CUid]

readPrec :: ReadPrec CUid

readListPrec :: ReadPrec [CUid]

Read Fd

Defined in GHC.Internal.System.Posix.Types

Methods

readsPrec :: Int -> ReadS Fd

readList :: ReadS [Fd]

readPrec :: ReadPrec Fd

readListPrec :: ReadPrec [Fd]

Read Lexeme

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Lexeme

readList :: ReadS [Lexeme]

readPrec :: ReadPrec Lexeme

readListPrec :: ReadPrec [Lexeme]

Read SomeChar

Defined in GHC.Internal.TypeLits

Methods

readsPrec :: Int -> ReadS SomeChar

readList :: ReadS [SomeChar]

readPrec :: ReadPrec SomeChar

readListPrec :: ReadPrec [SomeChar]

Read SomeSymbol

Since: base-4.7.0.0

Defined in GHC.Internal.TypeLits

Methods

readsPrec :: Int -> ReadS SomeSymbol

readList :: ReadS [SomeSymbol]

readPrec :: ReadPrec SomeSymbol

readListPrec :: ReadPrec [SomeSymbol]

Read SomeNat

Since: base-4.7.0.0

Defined in GHC.Internal.TypeNats

Methods

readsPrec :: Int -> ReadS SomeNat

readList :: ReadS [SomeNat]

readPrec :: ReadPrec SomeNat

readListPrec :: ReadPrec [SomeNat]

Read GeneralCategory

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS GeneralCategory

readList :: ReadS [GeneralCategory]

readPrec :: ReadPrec GeneralCategory

readListPrec :: ReadPrec [GeneralCategory]

Read Word16

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Word16

readList :: ReadS [Word16]

readPrec :: ReadPrec Word16

readListPrec :: ReadPrec [Word16]

Read Word32

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Word32

readList :: ReadS [Word32]

readPrec :: ReadPrec Word32

readListPrec :: ReadPrec [Word32]

Read Word64

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Word64

readList :: ReadS [Word64]

readPrec :: ReadPrec Word64

readListPrec :: ReadPrec [Word64]

Read Word8

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Word8

readList :: ReadS [Word8]

readPrec :: ReadPrec Word8

readListPrec :: ReadPrec [Word8]

Read Ordering

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Ordering

readList :: ReadS [Ordering]

readPrec :: ReadPrec Ordering

readListPrec :: ReadPrec [Ordering]

Read Integer

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Integer

readList :: ReadS [Integer]

readPrec :: ReadPrec Integer

readListPrec :: ReadPrec [Integer]

Read Natural

Since: base-4.8.0.0

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Natural

readList :: ReadS [Natural]

readPrec :: ReadPrec Natural

readListPrec :: ReadPrec [Natural]

Read ()

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS ()

readList :: ReadS [()]

readPrec :: ReadPrec ()

readListPrec :: ReadPrec [()]

Read Bool

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Bool

readList :: ReadS [Bool]

readPrec :: ReadPrec Bool

readListPrec :: ReadPrec [Bool]

Read Char

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Char

readList :: ReadS [Char]

readPrec :: ReadPrec Char

readListPrec :: ReadPrec [Char]

Read Double

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Double

readList :: ReadS [Double]

readPrec :: ReadPrec Double

readListPrec :: ReadPrec [Double]

Read Float

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Float

readList :: ReadS [Float]

readPrec :: ReadPrec Float

readListPrec :: ReadPrec [Float]

Read Int

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Int

readList :: ReadS [Int]

readPrec :: ReadPrec Int

readListPrec :: ReadPrec [Int]

Read Word

Since: base-4.5.0.0

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS Word

readList :: ReadS [Word]

readPrec :: ReadPrec Word

readListPrec :: ReadPrec [Word]

Read a => Read (Complex a)

Since: base-2.1

Defined in Data.Complex

Methods

readsPrec :: Int -> ReadS (Complex a)

readList :: ReadS [Complex a]

readPrec :: ReadPrec (Complex a)

readListPrec :: ReadPrec [Complex a]

Read a => Read (First a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

readsPrec :: Int -> ReadS (First a)

readList :: ReadS [First a]

readPrec :: ReadPrec (First a)

readListPrec :: ReadPrec [First a]

Read a => Read (Last a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

readsPrec :: Int -> ReadS (Last a)

readList :: ReadS [Last a]

readPrec :: ReadPrec (Last a)

readListPrec :: ReadPrec [Last a]

Read a => Read (Max a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

readsPrec :: Int -> ReadS (Max a)

readList :: ReadS [Max a]

readPrec :: ReadPrec (Max a)

readListPrec :: ReadPrec [Max a]

Read a => Read (Min a)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

readsPrec :: Int -> ReadS (Min a)

readList :: ReadS [Min a]

readPrec :: ReadPrec (Min a)

readListPrec :: ReadPrec [Min a]

Read m => Read (WrappedMonoid m)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

readsPrec :: Int -> ReadS (WrappedMonoid m)

readList :: ReadS [WrappedMonoid m]

readPrec :: ReadPrec (WrappedMonoid m)

readListPrec :: ReadPrec [WrappedMonoid m]

Read a => Read (NonEmpty a)

Since: base-4.11.0.0

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (NonEmpty a)

readList :: ReadS [NonEmpty a]

readPrec :: ReadPrec (NonEmpty a)

readListPrec :: ReadPrec [NonEmpty a]

Read a => Read (And a)

Since: base-4.16

Defined in GHC.Internal.Data.Bits

Methods

readsPrec :: Int -> ReadS (And a)

readList :: ReadS [And a]

readPrec :: ReadPrec (And a)

readListPrec :: ReadPrec [And a]

Read a => Read (Iff a)

Since: base-4.16

Defined in GHC.Internal.Data.Bits

Methods

readsPrec :: Int -> ReadS (Iff a)

readList :: ReadS [Iff a]

readPrec :: ReadPrec (Iff a)

readListPrec :: ReadPrec [Iff a]

Read a => Read (Ior a)

Since: base-4.16

Defined in GHC.Internal.Data.Bits

Methods

readsPrec :: Int -> ReadS (Ior a)

readList :: ReadS [Ior a]

readPrec :: ReadPrec (Ior a)

readListPrec :: ReadPrec [Ior a]

Read a => Read (Xor a)

Since: base-4.16

Defined in GHC.Internal.Data.Bits

Methods

readsPrec :: Int -> ReadS (Xor a)

readList :: ReadS [Xor a]

readPrec :: ReadPrec (Xor a)

readListPrec :: ReadPrec [Xor a]

Read a => Read (Identity a)

This instance would be equivalent to the derived instances of the Identity newtype if the runIdentity field were removed

Since: base-4.8.0.0

Defined in GHC.Internal.Data.Functor.Identity

Methods

readsPrec :: Int -> ReadS (Identity a)

readList :: ReadS [Identity a]

readPrec :: ReadPrec (Identity a)

readListPrec :: ReadPrec [Identity a]

Read a => Read (First a)

Since: base-2.1

Defined in GHC.Internal.Data.Monoid

Methods

readsPrec :: Int -> ReadS (First a)

readList :: ReadS [First a]

readPrec :: ReadPrec (First a)

readListPrec :: ReadPrec [First a]

Read a => Read (Last a)

Since: base-2.1

Defined in GHC.Internal.Data.Monoid

Methods

readsPrec :: Int -> ReadS (Last a)

readList :: ReadS [Last a]

readPrec :: ReadPrec (Last a)

readListPrec :: ReadPrec [Last a]

Read a => Read (Down a)

This instance would be equivalent to the derived instances of the Down newtype if the getDown field were removed

Since: base-4.7.0.0

Defined in GHC.Internal.Data.Ord

Methods

readsPrec :: Int -> ReadS (Down a)

readList :: ReadS [Down a]

readPrec :: ReadPrec (Down a)

readListPrec :: ReadPrec [Down a]

Read a => Read (Dual a)

Since: base-2.1

Defined in GHC.Internal.Data.Semigroup.Internal

Methods

readsPrec :: Int -> ReadS (Dual a)

readList :: ReadS [Dual a]

readPrec :: ReadPrec (Dual a)

readListPrec :: ReadPrec [Dual a]

Read a => Read (Product a)

Since: base-2.1

Defined in GHC.Internal.Data.Semigroup.Internal

Methods

readsPrec :: Int -> ReadS (Product a)

readList :: ReadS [Product a]

readPrec :: ReadPrec (Product a)

readListPrec :: ReadPrec [Product a]

Read a => Read (Sum a)

Since: base-2.1

Defined in GHC.Internal.Data.Semigroup.Internal

Methods

readsPrec :: Int -> ReadS (Sum a)

readList :: ReadS [Sum a]

readPrec :: ReadPrec (Sum a)

readListPrec :: ReadPrec [Sum a]

Read a => Read (ZipList a)

Since: base-4.7.0.0

Defined in GHC.Internal.Functor.ZipList

Methods

readsPrec :: Int -> ReadS (ZipList a)

readList :: ReadS [ZipList a]

readPrec :: ReadPrec (ZipList a)

readListPrec :: ReadPrec [ZipList a]

Read p => Read (Par1 p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS (Par1 p)

readList :: ReadS [Par1 p]

readPrec :: ReadPrec (Par1 p)

readListPrec :: ReadPrec [Par1 p]

(Integral a, Read a) => Read (Ratio a)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (Ratio a)

readList :: ReadS [Ratio a]

readPrec :: ReadPrec (Ratio a)

readListPrec :: ReadPrec [Ratio a]

Read a => Read (Maybe a)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (Maybe a)

readList :: ReadS [Maybe a]

readPrec :: ReadPrec (Maybe a)

readListPrec :: ReadPrec [Maybe a]

Read a => Read (Solo a)

Since: base-4.15

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (Solo a)

readList :: ReadS [Solo a]

readPrec :: ReadPrec (Solo a)

readListPrec :: ReadPrec [Solo a]

Read a => Read [a]

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS [a]

readList :: ReadS [[a]]

readPrec :: ReadPrec [a]

readListPrec :: ReadPrec [[a]]

HasResolution a => Read (Fixed a)

Since: base-4.3.0.0

Defined in Data.Fixed

Methods

readsPrec :: Int -> ReadS (Fixed a)

readList :: ReadS [Fixed a]

readPrec :: ReadPrec (Fixed a)

readListPrec :: ReadPrec [Fixed a]

(Read a, Read b) => Read (Arg a b)

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

readsPrec :: Int -> ReadS (Arg a b)

readList :: ReadS [Arg a b]

readPrec :: ReadPrec (Arg a b)

readListPrec :: ReadPrec [Arg a b]

(Ix a, Read a, Read b) => Read (Array a b)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (Array a b)

readList :: ReadS [Array a b]

readPrec :: ReadPrec (Array a b)

readListPrec :: ReadPrec [Array a b]

(Read a, Read b) => Read (Either a b)

Since: base-3.0

Defined in GHC.Internal.Data.Either

Methods

readsPrec :: Int -> ReadS (Either a b)

readList :: ReadS [Either a b]

readPrec :: ReadPrec (Either a b)

readListPrec :: ReadPrec [Either a b]

Read (Proxy t)

Since: base-4.7.0.0

Defined in GHC.Internal.Data.Proxy

Methods

readsPrec :: Int -> ReadS (Proxy t)

readList :: ReadS [Proxy t]

readPrec :: ReadPrec (Proxy t)

readListPrec :: ReadPrec [Proxy t]

Read (U1 p)

Since: base-4.9.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS (U1 p)

readList :: ReadS [U1 p]

readPrec :: ReadPrec (U1 p)

readListPrec :: ReadPrec [U1 p]

Read (V1 p)

Since: base-4.9.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS (V1 p)

readList :: ReadS [V1 p]

readPrec :: ReadPrec (V1 p)

readListPrec :: ReadPrec [V1 p]

(Read a, Read b) => Read (a, b)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b)

readList :: ReadS [(a, b)]

readPrec :: ReadPrec (a, b)

readListPrec :: ReadPrec [(a, b)]

Read a => Read (Const a b)

This instance would be equivalent to the derived instances of the Const newtype if the getConst field were removed

Since: base-4.8.0.0

Defined in GHC.Internal.Data.Functor.Const

Methods

readsPrec :: Int -> ReadS (Const a b)

readList :: ReadS [Const a b]

readPrec :: ReadPrec (Const a b)

readListPrec :: ReadPrec [Const a b]

Read (f a) => Read (Ap f a)

Since: base-4.12.0.0

Defined in GHC.Internal.Data.Monoid

Methods

readsPrec :: Int -> ReadS (Ap f a)

readList :: ReadS [Ap f a]

readPrec :: ReadPrec (Ap f a)

readListPrec :: ReadPrec [Ap f a]

Read (f a) => Read (Alt f a)

Since: base-4.8.0.0

Defined in GHC.Internal.Data.Semigroup.Internal

Methods

readsPrec :: Int -> ReadS (Alt f a)

readList :: ReadS [Alt f a]

readPrec :: ReadPrec (Alt f a)

readListPrec :: ReadPrec [Alt f a]

Coercible a b => Read (Coercion a b)

Since: base-4.7.0.0

Defined in GHC.Internal.Data.Type.Coercion

Methods

readsPrec :: Int -> ReadS (Coercion a b)

readList :: ReadS [Coercion a b]

readPrec :: ReadPrec (Coercion a b)

readListPrec :: ReadPrec [Coercion a b]

a ~ b => Read (a :~: b)

Since: base-4.7.0.0

Defined in GHC.Internal.Data.Type.Equality

Methods

readsPrec :: Int -> ReadS (a :~: b)

readList :: ReadS [a :~: b]

readPrec :: ReadPrec (a :~: b)

readListPrec :: ReadPrec [a :~: b]

Read (f p) => Read (Rec1 f p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS (Rec1 f p)

readList :: ReadS [Rec1 f p]

readPrec :: ReadPrec (Rec1 f p)

readListPrec :: ReadPrec [Rec1 f p]

(Read a, Read b, Read c) => Read (a, b, c)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c)

readList :: ReadS [(a, b, c)]

readPrec :: ReadPrec (a, b, c)

readListPrec :: ReadPrec [(a, b, c)]

(Read (f a), Read (g a)) => Read (Product f g a)

Since: base-4.18.0.0

Defined in Data.Functor.Product

Methods

readsPrec :: Int -> ReadS (Product f g a)

readList :: ReadS [Product f g a]

readPrec :: ReadPrec (Product f g a)

readListPrec :: ReadPrec [Product f g a]

(Read (f a), Read (g a)) => Read (Sum f g a)

Since: base-4.18.0.0

Defined in Data.Functor.Sum

Methods

readsPrec :: Int -> ReadS (Sum f g a)

readList :: ReadS [Sum f g a]

readPrec :: ReadPrec (Sum f g a)

readListPrec :: ReadPrec [Sum f g a]

a ~~ b => Read (a :~~: b)

Since: base-4.10.0.0

Defined in GHC.Internal.Data.Type.Equality

Methods

readsPrec :: Int -> ReadS (a :~~: b)

readList :: ReadS [a :~~: b]

readPrec :: ReadPrec (a :~~: b)

readListPrec :: ReadPrec [a :~~: b]

(Read (f p), Read (g p)) => Read ((f :*: g) p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS ((f :*: g) p)

readList :: ReadS [(f :*: g) p]

readPrec :: ReadPrec ((f :*: g) p)

readListPrec :: ReadPrec [(f :*: g) p]

(Read (f p), Read (g p)) => Read ((f :+: g) p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS ((f :+: g) p)

readList :: ReadS [(f :+: g) p]

readPrec :: ReadPrec ((f :+: g) p)

readListPrec :: ReadPrec [(f :+: g) p]

Read c => Read (K1 i c p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS (K1 i c p)

readList :: ReadS [K1 i c p]

readPrec :: ReadPrec (K1 i c p)

readListPrec :: ReadPrec [K1 i c p]

(Read a, Read b, Read c, Read d) => Read (a, b, c, d)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d)

readList :: ReadS [(a, b, c, d)]

readPrec :: ReadPrec (a, b, c, d)

readListPrec :: ReadPrec [(a, b, c, d)]

Read (f (g a)) => Read (Compose f g a)

Since: base-4.18.0.0

Defined in Data.Functor.Compose

Methods

readsPrec :: Int -> ReadS (Compose f g a)

readList :: ReadS [Compose f g a]

readPrec :: ReadPrec (Compose f g a)

readListPrec :: ReadPrec [Compose f g a]

Read (f (g p)) => Read ((f :.: g) p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS ((f :.: g) p)

readList :: ReadS [(f :.: g) p]

readPrec :: ReadPrec ((f :.: g) p)

readListPrec :: ReadPrec [(f :.: g) p]

Read (f p) => Read (M1 i c f p)

Since: base-4.7.0.0

Defined in GHC.Internal.Generics

Methods

readsPrec :: Int -> ReadS (M1 i c f p)

readList :: ReadS [M1 i c f p]

readPrec :: ReadPrec (M1 i c f p)

readListPrec :: ReadPrec [M1 i c f p]

(Read a, Read b, Read c, Read d, Read e) => Read (a, b, c, d, e)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e)

readList :: ReadS [(a, b, c, d, e)]

readPrec :: ReadPrec (a, b, c, d, e)

readListPrec :: ReadPrec [(a, b, c, d, e)]

(Read a, Read b, Read c, Read d, Read e, Read f) => Read (a, b, c, d, e, f)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f)

readList :: ReadS [(a, b, c, d, e, f)]

readPrec :: ReadPrec (a, b, c, d, e, f)

readListPrec :: ReadPrec [(a, b, c, d, e, f)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g) => Read (a, b, c, d, e, f, g)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g)

readList :: ReadS [(a, b, c, d, e, f, g)]

readPrec :: ReadPrec (a, b, c, d, e, f, g)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h) => Read (a, b, c, d, e, f, g, h)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h)

readList :: ReadS [(a, b, c, d, e, f, g, h)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i) => Read (a, b, c, d, e, f, g, h, i)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i)

readList :: ReadS [(a, b, c, d, e, f, g, h, i)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j) => Read (a, b, c, d, e, f, g, h, i, j)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j)

readList :: ReadS [(a, b, c, d, e, f, g, h, i, j)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k) => Read (a, b, c, d, e, f, g, h, i, j, k)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k)

readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l) => Read (a, b, c, d, e, f, g, h, i, j, k, l)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l)

readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l, Read m) => Read (a, b, c, d, e, f, g, h, i, j, k, l, m)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l, m)

readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l, m)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l, m)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l, m)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l, Read m, Read n) => Read (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)]

(Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h, Read i, Read j, Read k, Read l, Read m, Read n, Read o) => Read (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

Since: base-2.1

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)]

readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)]

ReadS type

type ReadS a = String -> [(a, String)]

A parser for a type a, represented as a function that takes a String and returns a list of possible parses as (a,String) pairs.

Note that this kind of backtracking parser is very inefficient; reading a large structure may be quite slow (cf ReadP).

Haskell 2010 compatibility

lex :: ReadS String

The lex function reads a single lexeme from the input, discarding initial white space, and returning the characters that constitute the lexeme. If the input string contains only white space, lex returns a single successful `lexeme' consisting of the empty string. (Thus lex "" = [("","")].) If there is no legal lexeme at the beginning of the input string, lex fails (i.e. returns []).

This lexer is not completely faithful to the Haskell lexical syntax in the following respects:

• Qualified names are not handled properly
• Octal and hexadecimal numerics are not recognized as a single token
• Comments are not treated properly

lexLitChar :: ReadS String

Read a string representation of a character, using Haskell source-language escape conventions. For example:

lexLitChar  "\\nHello"  =  [("\\n", "Hello")]

readLitChar :: ReadS Char

Read a string representation of a character, using Haskell source-language escape conventions, and convert it to the character that it encodes. For example:

readLitChar "\\nHello"  =  [('\n', "Hello")]

lexDigits :: ReadS String

Reads a non-empty string of decimal digits.

Defining readers

lexP :: ReadPrec Lexeme

Parse a single lexeme

expectP :: Lexeme -> ReadPrec ()

paren :: ReadPrec a -> ReadPrec a

(paren p) parses "(P0)" where p parses "P0" in precedence context zero

parens :: ReadPrec a -> ReadPrec a

(parens p) parses "P", "(P0)", "((P0))", etc, where p parses "P" in the current precedence context and parses "P0" in precedence context zero

list :: ReadPrec a -> ReadPrec [a]

(list p) parses a list of things parsed by p, using the usual square-bracket syntax.

choose :: [(String, ReadPrec a)] -> ReadPrec a

Parse the specified lexeme and continue as specified. Esp useful for nullary constructors; e.g. choose [("A", return A), ("B", return B)] We match both Ident and Symbol because the constructor might be an operator eg (:~:)

readListDefault :: Read a => ReadS [a]

A possible replacement definition for the readList method (GHC only). This is only needed for GHC, and even then only for Read instances where readListPrec isn't defined as readListPrecDefault.

readListPrecDefault :: Read a => ReadPrec [a]

A possible replacement definition for the readListPrec method, defined using readPrec (GHC only).

readNumber :: Num a => (Lexeme -> ReadPrec a) -> ReadPrec a

readField :: String -> ReadPrec a -> ReadPrec a

Read parser for a record field, of the form fieldName=value. The fieldName must be an alphanumeric identifier; for symbols (operator-style) field names, e.g. (#), use readSymField). The second argument is a parser for the field value.

readFieldHash :: String -> ReadPrec a -> ReadPrec a

Read parser for a record field, of the form fieldName#=value. That is, an alphanumeric identifier fieldName followed by the symbol #. The second argument is a parser for the field value.

Note that readField does not suffice for this purpose due to #5041.

readSymField :: String -> ReadPrec a -> ReadPrec a

Read parser for a symbol record field, of the form (###)=value (where ### is the field name). The field name must be a symbol (operator-style), e.g. (#). For regular (alphanumeric) field names, use readField. The second argument is a parser for the field value.

readParen :: Bool -> ReadS a -> ReadS a

readParen True p parses what p parses, but surrounded with parentheses.

readParen False p parses what p parses, but optionally surrounded with parentheses.