Text.Read

Copyright	(c) The University of Glasgow 2001
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	libraries@haskell.org
Stability	provisional
Portability	non-portable (uses Text.ParserCombinators.ReadP)
Safe Haskell	Safe
Language	Haskell2010

The Read class
Haskell 2010 functions
New parsing functions

Description

Converting strings to values.

The Text.Read module is the canonical place to import for Read-class facilities. For GHC only, it offers an extended and much improved Read class, which constitutes a proposed alternative to the Haskell 2010 Read. In particular, writing parsers is easier, and the parsers are much more efficient.

The Read class

class Read a where Source

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 Source

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] Source

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 Source

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

readListPrec :: ReadPrec [a] Source

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

Instances details

Read GCDetails Source	Since: base-4.10.0.0
Instance details Defined in GHC.Stats Methods readsPrec :: Int -> ReadS GCDetails Source readList :: ReadS [GCDetails] Source readPrec :: ReadPrec GCDetails Source readListPrec :: ReadPrec [GCDetails] Source
Read RTSStats Source	Since: base-4.10.0.0
Instance details Defined in GHC.Stats Methods readsPrec :: Int -> ReadS RTSStats Source readList :: ReadS [RTSStats] Source readPrec :: ReadPrec RTSStats Source readListPrec :: ReadPrec [RTSStats] Source
Read Void Source	Reading a `Void` value is always a parse error, considering `Void` as a data type with no constructors. Since: base-4.8.0.0
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Void Source readList :: ReadS [Void] Source readPrec :: ReadPrec Void Source readListPrec :: ReadPrec [Void] Source
Read ByteOrder Source	Since: base-4.11.0.0
Instance details Defined in GHC.Internal.ByteOrder Methods readsPrec :: Int -> ReadS ByteOrder Source readList :: ReadS [ByteOrder] Source readPrec :: ReadPrec ByteOrder Source readListPrec :: ReadPrec [ByteOrder] Source
Read All Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods readsPrec :: Int -> ReadS All Source readList :: ReadS [All] Source readPrec :: ReadPrec All Source readListPrec :: ReadPrec [All] Source
Read Any Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods readsPrec :: Int -> ReadS Any Source readList :: ReadS [Any] Source readPrec :: ReadPrec Any Source readListPrec :: ReadPrec [Any] Source
Read Version Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Version Methods readsPrec :: Int -> ReadS Version Source readList :: ReadS [Version] Source readPrec :: ReadPrec Version Source readListPrec :: ReadPrec [Version] Source
Read CBool Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CBool Source readList :: ReadS [CBool] Source readPrec :: ReadPrec CBool Source readListPrec :: ReadPrec [CBool] Source
Read CChar Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CChar Source readList :: ReadS [CChar] Source readPrec :: ReadPrec CChar Source readListPrec :: ReadPrec [CChar] Source
Read CClock Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CClock Source readList :: ReadS [CClock] Source readPrec :: ReadPrec CClock Source readListPrec :: ReadPrec [CClock] Source
Read CDouble Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CDouble Source readList :: ReadS [CDouble] Source readPrec :: ReadPrec CDouble Source readListPrec :: ReadPrec [CDouble] Source
Read CFloat Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CFloat Source readList :: ReadS [CFloat] Source readPrec :: ReadPrec CFloat Source readListPrec :: ReadPrec [CFloat] Source
Read CInt Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CInt Source readList :: ReadS [CInt] Source readPrec :: ReadPrec CInt Source readListPrec :: ReadPrec [CInt] Source
Read CIntMax Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CIntMax Source readList :: ReadS [CIntMax] Source readPrec :: ReadPrec CIntMax Source readListPrec :: ReadPrec [CIntMax] Source
Read CIntPtr Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CIntPtr Source readList :: ReadS [CIntPtr] Source readPrec :: ReadPrec CIntPtr Source readListPrec :: ReadPrec [CIntPtr] Source
Read CLLong Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CLLong Source readList :: ReadS [CLLong] Source readPrec :: ReadPrec CLLong Source readListPrec :: ReadPrec [CLLong] Source
Read CLong Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CLong Source readList :: ReadS [CLong] Source readPrec :: ReadPrec CLong Source readListPrec :: ReadPrec [CLong] Source
Read CPtrdiff Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CPtrdiff Source readList :: ReadS [CPtrdiff] Source readPrec :: ReadPrec CPtrdiff Source readListPrec :: ReadPrec [CPtrdiff] Source
Read CSChar Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CSChar Source readList :: ReadS [CSChar] Source readPrec :: ReadPrec CSChar Source readListPrec :: ReadPrec [CSChar] Source
Read CSUSeconds Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CSUSeconds Source readList :: ReadS [CSUSeconds] Source readPrec :: ReadPrec CSUSeconds Source readListPrec :: ReadPrec [CSUSeconds] Source
Read CShort Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CShort Source readList :: ReadS [CShort] Source readPrec :: ReadPrec CShort Source readListPrec :: ReadPrec [CShort] Source
Read CSigAtomic Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CSigAtomic Source readList :: ReadS [CSigAtomic] Source readPrec :: ReadPrec CSigAtomic Source readListPrec :: ReadPrec [CSigAtomic] Source
Read CSize Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CSize Source readList :: ReadS [CSize] Source readPrec :: ReadPrec CSize Source readListPrec :: ReadPrec [CSize] Source
Read CTime Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CTime Source readList :: ReadS [CTime] Source readPrec :: ReadPrec CTime Source readListPrec :: ReadPrec [CTime] Source
Read CUChar Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CUChar Source readList :: ReadS [CUChar] Source readPrec :: ReadPrec CUChar Source readListPrec :: ReadPrec [CUChar] Source
Read CUInt Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CUInt Source readList :: ReadS [CUInt] Source readPrec :: ReadPrec CUInt Source readListPrec :: ReadPrec [CUInt] Source
Read CUIntMax Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CUIntMax Source readList :: ReadS [CUIntMax] Source readPrec :: ReadPrec CUIntMax Source readListPrec :: ReadPrec [CUIntMax] Source
Read CUIntPtr Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CUIntPtr Source readList :: ReadS [CUIntPtr] Source readPrec :: ReadPrec CUIntPtr Source readListPrec :: ReadPrec [CUIntPtr] Source
Read CULLong Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CULLong Source readList :: ReadS [CULLong] Source readPrec :: ReadPrec CULLong Source readListPrec :: ReadPrec [CULLong] Source
Read CULong Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CULong Source readList :: ReadS [CULong] Source readPrec :: ReadPrec CULong Source readListPrec :: ReadPrec [CULong] Source
Read CUSeconds Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CUSeconds Source readList :: ReadS [CUSeconds] Source readPrec :: ReadPrec CUSeconds Source readListPrec :: ReadPrec [CUSeconds] Source
Read CUShort Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CUShort Source readList :: ReadS [CUShort] Source readPrec :: ReadPrec CUShort Source readListPrec :: ReadPrec [CUShort] Source
Read CWchar Source
Instance details Defined in GHC.Internal.Foreign.C.Types Methods readsPrec :: Int -> ReadS CWchar Source readList :: ReadS [CWchar] Source readPrec :: ReadPrec CWchar Source readListPrec :: ReadPrec [CWchar] Source
Read IntPtr Source
Instance details Defined in GHC.Internal.Foreign.Ptr Methods readsPrec :: Int -> ReadS IntPtr Source readList :: ReadS [IntPtr] Source readPrec :: ReadPrec IntPtr Source readListPrec :: ReadPrec [IntPtr] Source
Read WordPtr Source
Instance details Defined in GHC.Internal.Foreign.Ptr Methods readsPrec :: Int -> ReadS WordPtr Source readList :: ReadS [WordPtr] Source readPrec :: ReadPrec WordPtr Source readListPrec :: ReadPrec [WordPtr] Source
Read Associativity Source	Since: base-4.6.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS Associativity Source readList :: ReadS [Associativity] Source readPrec :: ReadPrec Associativity Source readListPrec :: ReadPrec [Associativity] Source
Read DecidedStrictness Source	Since: base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS DecidedStrictness Source readList :: ReadS [DecidedStrictness] Source readPrec :: ReadPrec DecidedStrictness Source readListPrec :: ReadPrec [DecidedStrictness] Source
Read Fixity Source	Since: base-4.6.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS Fixity Source readList :: ReadS [Fixity] Source readPrec :: ReadPrec Fixity Source readListPrec :: ReadPrec [Fixity] Source
Read SourceStrictness Source	Since: base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS SourceStrictness Source readList :: ReadS [SourceStrictness] Source readPrec :: ReadPrec SourceStrictness Source readListPrec :: ReadPrec [SourceStrictness] Source
Read SourceUnpackedness Source	Since: base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS SourceUnpackedness Source readList :: ReadS [SourceUnpackedness] Source readPrec :: ReadPrec SourceUnpackedness Source readListPrec :: ReadPrec [SourceUnpackedness] Source
Read SeekMode Source	Since: base-4.2.0.0
Instance details Defined in GHC.Internal.IO.Device Methods readsPrec :: Int -> ReadS SeekMode Source readList :: ReadS [SeekMode] Source readPrec :: ReadPrec SeekMode Source readListPrec :: ReadPrec [SeekMode] Source
Read ExitCode Source
Instance details Defined in GHC.Internal.IO.Exception Methods readsPrec :: Int -> ReadS ExitCode Source readList :: ReadS [ExitCode] Source readPrec :: ReadPrec ExitCode Source readListPrec :: ReadPrec [ExitCode] Source
Read BufferMode Source	Since: base-4.2.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods readsPrec :: Int -> ReadS BufferMode Source readList :: ReadS [BufferMode] Source readPrec :: ReadPrec BufferMode Source readListPrec :: ReadPrec [BufferMode] Source
Read Newline Source	Since: base-4.3.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods readsPrec :: Int -> ReadS Newline Source readList :: ReadS [Newline] Source readPrec :: ReadPrec Newline Source readListPrec :: ReadPrec [Newline] Source
Read NewlineMode Source	Since: base-4.3.0.0
Instance details Defined in GHC.Internal.IO.Handle.Types Methods readsPrec :: Int -> ReadS NewlineMode Source readList :: ReadS [NewlineMode] Source readPrec :: ReadPrec NewlineMode Source readListPrec :: ReadPrec [NewlineMode] Source
Read IOMode Source	Since: base-4.2.0.0
Instance details Defined in GHC.Internal.IO.IOMode Methods readsPrec :: Int -> ReadS IOMode Source readList :: ReadS [IOMode] Source readPrec :: ReadPrec IOMode Source readListPrec :: ReadPrec [IOMode] Source
Read Int16 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Int Methods readsPrec :: Int -> ReadS Int16 Source readList :: ReadS [Int16] Source readPrec :: ReadPrec Int16 Source readListPrec :: ReadPrec [Int16] Source
Read Int32 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Int Methods readsPrec :: Int -> ReadS Int32 Source readList :: ReadS [Int32] Source readPrec :: ReadPrec Int32 Source readListPrec :: ReadPrec [Int32] Source
Read Int64 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Int Methods readsPrec :: Int -> ReadS Int64 Source readList :: ReadS [Int64] Source readPrec :: ReadPrec Int64 Source readListPrec :: ReadPrec [Int64] Source
Read Int8 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Int Methods readsPrec :: Int -> ReadS Int8 Source readList :: ReadS [Int8] Source readPrec :: ReadPrec Int8 Source readListPrec :: ReadPrec [Int8] Source
Read GCDetails Source	Since: base-4.10.0.0
Instance details Defined in GHC.Internal.Stats Methods readsPrec :: Int -> ReadS GCDetails Source readList :: ReadS [GCDetails] Source readPrec :: ReadPrec GCDetails Source readListPrec :: ReadPrec [GCDetails] Source
Read RTSStats Source	Since: base-4.10.0.0
Instance details Defined in GHC.Internal.Stats Methods readsPrec :: Int -> ReadS RTSStats Source readList :: ReadS [RTSStats] Source readPrec :: ReadPrec RTSStats Source readListPrec :: ReadPrec [RTSStats] Source
Read CBlkCnt Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CBlkCnt Source readList :: ReadS [CBlkCnt] Source readPrec :: ReadPrec CBlkCnt Source readListPrec :: ReadPrec [CBlkCnt] Source
Read CBlkSize Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CBlkSize Source readList :: ReadS [CBlkSize] Source readPrec :: ReadPrec CBlkSize Source readListPrec :: ReadPrec [CBlkSize] Source
Read CCc Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CCc Source readList :: ReadS [CCc] Source readPrec :: ReadPrec CCc Source readListPrec :: ReadPrec [CCc] Source
Read CClockId Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CClockId Source readList :: ReadS [CClockId] Source readPrec :: ReadPrec CClockId Source readListPrec :: ReadPrec [CClockId] Source
Read CDev Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CDev Source readList :: ReadS [CDev] Source readPrec :: ReadPrec CDev Source readListPrec :: ReadPrec [CDev] Source
Read CFsBlkCnt Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CFsBlkCnt Source readList :: ReadS [CFsBlkCnt] Source readPrec :: ReadPrec CFsBlkCnt Source readListPrec :: ReadPrec [CFsBlkCnt] Source
Read CFsFilCnt Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CFsFilCnt Source readList :: ReadS [CFsFilCnt] Source readPrec :: ReadPrec CFsFilCnt Source readListPrec :: ReadPrec [CFsFilCnt] Source
Read CGid Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CGid Source readList :: ReadS [CGid] Source readPrec :: ReadPrec CGid Source readListPrec :: ReadPrec [CGid] Source
Read CId Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CId Source readList :: ReadS [CId] Source readPrec :: ReadPrec CId Source readListPrec :: ReadPrec [CId] Source
Read CIno Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CIno Source readList :: ReadS [CIno] Source readPrec :: ReadPrec CIno Source readListPrec :: ReadPrec [CIno] Source
Read CKey Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CKey Source readList :: ReadS [CKey] Source readPrec :: ReadPrec CKey Source readListPrec :: ReadPrec [CKey] Source
Read CMode Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CMode Source readList :: ReadS [CMode] Source readPrec :: ReadPrec CMode Source readListPrec :: ReadPrec [CMode] Source
Read CNfds Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CNfds Source readList :: ReadS [CNfds] Source readPrec :: ReadPrec CNfds Source readListPrec :: ReadPrec [CNfds] Source
Read CNlink Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CNlink Source readList :: ReadS [CNlink] Source readPrec :: ReadPrec CNlink Source readListPrec :: ReadPrec [CNlink] Source
Read COff Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS COff Source readList :: ReadS [COff] Source readPrec :: ReadPrec COff Source readListPrec :: ReadPrec [COff] Source
Read CPid Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CPid Source readList :: ReadS [CPid] Source readPrec :: ReadPrec CPid Source readListPrec :: ReadPrec [CPid] Source
Read CRLim Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CRLim Source readList :: ReadS [CRLim] Source readPrec :: ReadPrec CRLim Source readListPrec :: ReadPrec [CRLim] Source
Read CSocklen Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CSocklen Source readList :: ReadS [CSocklen] Source readPrec :: ReadPrec CSocklen Source readListPrec :: ReadPrec [CSocklen] Source
Read CSpeed Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CSpeed Source readList :: ReadS [CSpeed] Source readPrec :: ReadPrec CSpeed Source readListPrec :: ReadPrec [CSpeed] Source
Read CSsize Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CSsize Source readList :: ReadS [CSsize] Source readPrec :: ReadPrec CSsize Source readListPrec :: ReadPrec [CSsize] Source
Read CTcflag Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CTcflag Source readList :: ReadS [CTcflag] Source readPrec :: ReadPrec CTcflag Source readListPrec :: ReadPrec [CTcflag] Source
Read CUid Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS CUid Source readList :: ReadS [CUid] Source readPrec :: ReadPrec CUid Source readListPrec :: ReadPrec [CUid] Source
Read Fd Source
Instance details Defined in GHC.Internal.System.Posix.Types Methods readsPrec :: Int -> ReadS Fd Source readList :: ReadS [Fd] Source readPrec :: ReadPrec Fd Source readListPrec :: ReadPrec [Fd] Source
Read Lexeme Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Lexeme Source readList :: ReadS [Lexeme] Source readPrec :: ReadPrec Lexeme Source readListPrec :: ReadPrec [Lexeme] Source
Read SomeChar Source
Instance details Defined in GHC.Internal.TypeLits Methods readsPrec :: Int -> ReadS SomeChar Source readList :: ReadS [SomeChar] Source readPrec :: ReadPrec SomeChar Source readListPrec :: ReadPrec [SomeChar] Source
Read SomeSymbol Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.TypeLits Methods readsPrec :: Int -> ReadS SomeSymbol Source readList :: ReadS [SomeSymbol] Source readPrec :: ReadPrec SomeSymbol Source readListPrec :: ReadPrec [SomeSymbol] Source
Read SomeNat Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.TypeNats Methods readsPrec :: Int -> ReadS SomeNat Source readList :: ReadS [SomeNat] Source readPrec :: ReadPrec SomeNat Source readListPrec :: ReadPrec [SomeNat] Source
Read Ordering Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Ordering Source readList :: ReadS [Ordering] Source readPrec :: ReadPrec Ordering Source readListPrec :: ReadPrec [Ordering] Source
Read GeneralCategory Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS GeneralCategory Source readList :: ReadS [GeneralCategory] Source readPrec :: ReadPrec GeneralCategory Source readListPrec :: ReadPrec [GeneralCategory] Source
Read Word16 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Word16 Source readList :: ReadS [Word16] Source readPrec :: ReadPrec Word16 Source readListPrec :: ReadPrec [Word16] Source
Read Word32 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Word32 Source readList :: ReadS [Word32] Source readPrec :: ReadPrec Word32 Source readListPrec :: ReadPrec [Word32] Source
Read Word64 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Word64 Source readList :: ReadS [Word64] Source readPrec :: ReadPrec Word64 Source readListPrec :: ReadPrec [Word64] Source
Read Word8 Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Word8 Source readList :: ReadS [Word8] Source readPrec :: ReadPrec Word8 Source readListPrec :: ReadPrec [Word8] Source
Read Integer Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Integer Source readList :: ReadS [Integer] Source readPrec :: ReadPrec Integer Source readListPrec :: ReadPrec [Integer] Source
Read Natural Source	Since: base-4.8.0.0
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Natural Source readList :: ReadS [Natural] Source readPrec :: ReadPrec Natural Source readListPrec :: ReadPrec [Natural] Source
Read () Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS () Source readList :: ReadS [()] Source readPrec :: ReadPrec () Source readListPrec :: ReadPrec [()] Source
Read Bool Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Bool Source readList :: ReadS [Bool] Source readPrec :: ReadPrec Bool Source readListPrec :: ReadPrec [Bool] Source
Read Char Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Char Source readList :: ReadS [Char] Source readPrec :: ReadPrec Char Source readListPrec :: ReadPrec [Char] Source
Read Double Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Double Source readList :: ReadS [Double] Source readPrec :: ReadPrec Double Source readListPrec :: ReadPrec [Double] Source
Read Float Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Float Source readList :: ReadS [Float] Source readPrec :: ReadPrec Float Source readListPrec :: ReadPrec [Float] Source
Read Int Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Int Source readList :: ReadS [Int] Source readPrec :: ReadPrec Int Source readListPrec :: ReadPrec [Int] Source
Read Word Source	Since: base-4.5.0.0
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Word Source readList :: ReadS [Word] Source readPrec :: ReadPrec Word Source readListPrec :: ReadPrec [Word] Source
Read a => Read (Complex a) Source	Since: base-2.1
Instance details Defined in Data.Complex Methods readsPrec :: Int -> ReadS (Complex a) Source readList :: ReadS [Complex a] Source readPrec :: ReadPrec (Complex a) Source readListPrec :: ReadPrec [Complex a] Source
Read a => Read (First a) Source	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods readsPrec :: Int -> ReadS (First a) Source readList :: ReadS [First a] Source readPrec :: ReadPrec (First a) Source readListPrec :: ReadPrec [First a] Source
Read a => Read (Last a) Source	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods readsPrec :: Int -> ReadS (Last a) Source readList :: ReadS [Last a] Source readPrec :: ReadPrec (Last a) Source readListPrec :: ReadPrec [Last a] Source
Read a => Read (Max a) Source	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods readsPrec :: Int -> ReadS (Max a) Source readList :: ReadS [Max a] Source readPrec :: ReadPrec (Max a) Source readListPrec :: ReadPrec [Max a] Source
Read a => Read (Min a) Source	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods readsPrec :: Int -> ReadS (Min a) Source readList :: ReadS [Min a] Source readPrec :: ReadPrec (Min a) Source readListPrec :: ReadPrec [Min a] Source
Read m => Read (WrappedMonoid m) Source	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods readsPrec :: Int -> ReadS (WrappedMonoid m) Source readList :: ReadS [WrappedMonoid m] Source readPrec :: ReadPrec (WrappedMonoid m) Source readListPrec :: ReadPrec [WrappedMonoid m] Source
Read a => Read (NonEmpty a) Source	Since: base-4.11.0.0
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (NonEmpty a) Source readList :: ReadS [NonEmpty a] Source readPrec :: ReadPrec (NonEmpty a) Source readListPrec :: ReadPrec [NonEmpty a] Source
Read a => Read (And a) Source	Since: base-4.16
Instance details Defined in GHC.Internal.Data.Bits Methods readsPrec :: Int -> ReadS (And a) Source readList :: ReadS [And a] Source readPrec :: ReadPrec (And a) Source readListPrec :: ReadPrec [And a] Source
Read a => Read (Iff a) Source	Since: base-4.16
Instance details Defined in GHC.Internal.Data.Bits Methods readsPrec :: Int -> ReadS (Iff a) Source readList :: ReadS [Iff a] Source readPrec :: ReadPrec (Iff a) Source readListPrec :: ReadPrec [Iff a] Source
Read a => Read (Ior a) Source	Since: base-4.16
Instance details Defined in GHC.Internal.Data.Bits Methods readsPrec :: Int -> ReadS (Ior a) Source readList :: ReadS [Ior a] Source readPrec :: ReadPrec (Ior a) Source readListPrec :: ReadPrec [Ior a] Source
Read a => Read (Xor a) Source	Since: base-4.16
Instance details Defined in GHC.Internal.Data.Bits Methods readsPrec :: Int -> ReadS (Xor a) Source readList :: ReadS [Xor a] Source readPrec :: ReadPrec (Xor a) Source readListPrec :: ReadPrec [Xor a] Source
Read a => Read (Identity a) Source	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
Instance details Defined in GHC.Internal.Data.Functor.Identity Methods readsPrec :: Int -> ReadS (Identity a) Source readList :: ReadS [Identity a] Source readPrec :: ReadPrec (Identity a) Source readListPrec :: ReadPrec [Identity a] Source
Read a => Read (First a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Monoid Methods readsPrec :: Int -> ReadS (First a) Source readList :: ReadS [First a] Source readPrec :: ReadPrec (First a) Source readListPrec :: ReadPrec [First a] Source
Read a => Read (Last a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Monoid Methods readsPrec :: Int -> ReadS (Last a) Source readList :: ReadS [Last a] Source readPrec :: ReadPrec (Last a) Source readListPrec :: ReadPrec [Last a] Source
Read a => Read (Down a) Source	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
Instance details Defined in GHC.Internal.Data.Ord Methods readsPrec :: Int -> ReadS (Down a) Source readList :: ReadS [Down a] Source readPrec :: ReadPrec (Down a) Source readListPrec :: ReadPrec [Down a] Source
Read a => Read (Dual a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods readsPrec :: Int -> ReadS (Dual a) Source readList :: ReadS [Dual a] Source readPrec :: ReadPrec (Dual a) Source readListPrec :: ReadPrec [Dual a] Source
Read a => Read (Product a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods readsPrec :: Int -> ReadS (Product a) Source readList :: ReadS [Product a] Source readPrec :: ReadPrec (Product a) Source readListPrec :: ReadPrec [Product a] Source
Read a => Read (Sum a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods readsPrec :: Int -> ReadS (Sum a) Source readList :: ReadS [Sum a] Source readPrec :: ReadPrec (Sum a) Source readListPrec :: ReadPrec [Sum a] Source
Read a => Read (ZipList a) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Functor.ZipList Methods readsPrec :: Int -> ReadS (ZipList a) Source readList :: ReadS [ZipList a] Source readPrec :: ReadPrec (ZipList a) Source readListPrec :: ReadPrec [ZipList a] Source
Read p => Read (Par1 p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS (Par1 p) Source readList :: ReadS [Par1 p] Source readPrec :: ReadPrec (Par1 p) Source readListPrec :: ReadPrec [Par1 p] Source
(Integral a, Read a) => Read (Ratio a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (Ratio a) Source readList :: ReadS [Ratio a] Source readPrec :: ReadPrec (Ratio a) Source readListPrec :: ReadPrec [Ratio a] Source
Read a => Read (Maybe a) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (Maybe a) Source readList :: ReadS [Maybe a] Source readPrec :: ReadPrec (Maybe a) Source readListPrec :: ReadPrec [Maybe a] Source
Read a => Read (Solo a) Source	Since: base-4.15
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (Solo a) Source readList :: ReadS [Solo a] Source readPrec :: ReadPrec (Solo a) Source readListPrec :: ReadPrec [Solo a] Source
Read a => Read [a] Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS [a] Source readList :: ReadS [[a]] Source readPrec :: ReadPrec [a] Source readListPrec :: ReadPrec [[a]] Source
HasResolution a => Read (Fixed a) Source	Since: base-4.3.0.0
Instance details Defined in Data.Fixed Methods readsPrec :: Int -> ReadS (Fixed a) Source readList :: ReadS [Fixed a] Source readPrec :: ReadPrec (Fixed a) Source readListPrec :: ReadPrec [Fixed a] Source
(Read a, Read b) => Read (Arg a b) Source	Since: base-4.9.0.0
Instance details Defined in Data.Semigroup Methods readsPrec :: Int -> ReadS (Arg a b) Source readList :: ReadS [Arg a b] Source readPrec :: ReadPrec (Arg a b) Source readListPrec :: ReadPrec [Arg a b] Source
(Ix a, Read a, Read b) => Read (Array a b) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (Array a b) Source readList :: ReadS [Array a b] Source readPrec :: ReadPrec (Array a b) Source readListPrec :: ReadPrec [Array a b] Source
(Read a, Read b) => Read (Either a b) Source	Since: base-3.0
Instance details Defined in GHC.Internal.Data.Either Methods readsPrec :: Int -> ReadS (Either a b) Source readList :: ReadS [Either a b] Source readPrec :: ReadPrec (Either a b) Source readListPrec :: ReadPrec [Either a b] Source
Read (Proxy t) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Proxy Methods readsPrec :: Int -> ReadS (Proxy t) Source readList :: ReadS [Proxy t] Source readPrec :: ReadPrec (Proxy t) Source readListPrec :: ReadPrec [Proxy t] Source
Read (U1 p) Source	Since: base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS (U1 p) Source readList :: ReadS [U1 p] Source readPrec :: ReadPrec (U1 p) Source readListPrec :: ReadPrec [U1 p] Source
Read (V1 p) Source	Since: base-4.9.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS (V1 p) Source readList :: ReadS [V1 p] Source readPrec :: ReadPrec (V1 p) Source readListPrec :: ReadPrec [V1 p] Source
(Read a, Read b) => Read (a, b) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b) Source readList :: ReadS [(a, b)] Source readPrec :: ReadPrec (a, b) Source readListPrec :: ReadPrec [(a, b)] Source
Read a => Read (Const a b) Source	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
Instance details Defined in GHC.Internal.Data.Functor.Const Methods readsPrec :: Int -> ReadS (Const a b) Source readList :: ReadS [Const a b] Source readPrec :: ReadPrec (Const a b) Source readListPrec :: ReadPrec [Const a b] Source
Read (f a) => Read (Ap f a) Source	Since: base-4.12.0.0
Instance details Defined in GHC.Internal.Data.Monoid Methods readsPrec :: Int -> ReadS (Ap f a) Source readList :: ReadS [Ap f a] Source readPrec :: ReadPrec (Ap f a) Source readListPrec :: ReadPrec [Ap f a] Source
Read (f a) => Read (Alt f a) Source	Since: base-4.8.0.0
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods readsPrec :: Int -> ReadS (Alt f a) Source readList :: ReadS [Alt f a] Source readPrec :: ReadPrec (Alt f a) Source readListPrec :: ReadPrec [Alt f a] Source
Coercible a b => Read (Coercion a b) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Type.Coercion Methods readsPrec :: Int -> ReadS (Coercion a b) Source readList :: ReadS [Coercion a b] Source readPrec :: ReadPrec (Coercion a b) Source readListPrec :: ReadPrec [Coercion a b] Source
a ~ b => Read (a :~: b) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Data.Type.Equality Methods readsPrec :: Int -> ReadS (a :~: b) Source readList :: ReadS [a :~: b] Source readPrec :: ReadPrec (a :~: b) Source readListPrec :: ReadPrec [a :~: b] Source
Read (f p) => Read (Rec1 f p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS (Rec1 f p) Source readList :: ReadS [Rec1 f p] Source readPrec :: ReadPrec (Rec1 f p) Source readListPrec :: ReadPrec [Rec1 f p] Source
(Read a, Read b, Read c) => Read (a, b, c) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c) Source readList :: ReadS [(a, b, c)] Source readPrec :: ReadPrec (a, b, c) Source readListPrec :: ReadPrec [(a, b, c)] Source
(Read (f a), Read (g a)) => Read (Product f g a) Source	Since: base-4.18.0.0
Instance details Defined in Data.Functor.Product Methods readsPrec :: Int -> ReadS (Product f g a) Source readList :: ReadS [Product f g a] Source readPrec :: ReadPrec (Product f g a) Source readListPrec :: ReadPrec [Product f g a] Source
(Read (f a), Read (g a)) => Read (Sum f g a) Source	Since: base-4.18.0.0
Instance details Defined in Data.Functor.Sum Methods readsPrec :: Int -> ReadS (Sum f g a) Source readList :: ReadS [Sum f g a] Source readPrec :: ReadPrec (Sum f g a) Source readListPrec :: ReadPrec [Sum f g a] Source
a ~~ b => Read (a :~~: b) Source	Since: base-4.10.0.0
Instance details Defined in GHC.Internal.Data.Type.Equality Methods readsPrec :: Int -> ReadS (a :~~: b) Source readList :: ReadS [a :~~: b] Source readPrec :: ReadPrec (a :~~: b) Source readListPrec :: ReadPrec [a :~~: b] Source
(Read (f p), Read (g p)) => Read ((f :*: g) p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS ((f :: g) p) Source readList :: ReadS [(f :: g) p] Source readPrec :: ReadPrec ((f :: g) p) Source readListPrec :: ReadPrec [(f :: g) p] Source
(Read (f p), Read (g p)) => Read ((f :+: g) p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS ((f :+: g) p) Source readList :: ReadS [(f :+: g) p] Source readPrec :: ReadPrec ((f :+: g) p) Source readListPrec :: ReadPrec [(f :+: g) p] Source
Read c => Read (K1 i c p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS (K1 i c p) Source readList :: ReadS [K1 i c p] Source readPrec :: ReadPrec (K1 i c p) Source readListPrec :: ReadPrec [K1 i c p] Source
(Read a, Read b, Read c, Read d) => Read (a, b, c, d) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d) Source readList :: ReadS [(a, b, c, d)] Source readPrec :: ReadPrec (a, b, c, d) Source readListPrec :: ReadPrec [(a, b, c, d)] Source
Read (f (g a)) => Read (Compose f g a) Source	Since: base-4.18.0.0
Instance details Defined in Data.Functor.Compose Methods readsPrec :: Int -> ReadS (Compose f g a) Source readList :: ReadS [Compose f g a] Source readPrec :: ReadPrec (Compose f g a) Source readListPrec :: ReadPrec [Compose f g a] Source
Read (f (g p)) => Read ((f :.: g) p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS ((f :.: g) p) Source readList :: ReadS [(f :.: g) p] Source readPrec :: ReadPrec ((f :.: g) p) Source readListPrec :: ReadPrec [(f :.: g) p] Source
Read (f p) => Read (M1 i c f p) Source	Since: base-4.7.0.0
Instance details Defined in GHC.Internal.Generics Methods readsPrec :: Int -> ReadS (M1 i c f p) Source readList :: ReadS [M1 i c f p] Source readPrec :: ReadPrec (M1 i c f p) Source readListPrec :: ReadPrec [M1 i c f p] Source
(Read a, Read b, Read c, Read d, Read e) => Read (a, b, c, d, e) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e) Source readList :: ReadS [(a, b, c, d, e)] Source readPrec :: ReadPrec (a, b, c, d, e) Source readListPrec :: ReadPrec [(a, b, c, d, e)] Source
(Read a, Read b, Read c, Read d, Read e, Read f) => Read (a, b, c, d, e, f) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f) Source readList :: ReadS [(a, b, c, d, e, f)] Source readPrec :: ReadPrec (a, b, c, d, e, f) Source readListPrec :: ReadPrec [(a, b, c, d, e, f)] Source
(Read a, Read b, Read c, Read d, Read e, Read f, Read g) => Read (a, b, c, d, e, f, g) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g) Source readList :: ReadS [(a, b, c, d, e, f, g)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h) Source readList :: ReadS [(a, b, c, d, e, f, g, h)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i, j)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l, m) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l, m)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l, m) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l, m)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l, m, n) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l, m, n) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l, m, n)] Source
(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) Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) Source readList :: ReadS [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)] Source readPrec :: ReadPrec (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) Source readListPrec :: ReadPrec [(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)] Source

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

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 functions

reads :: Read a => ReadS a Source

equivalent to readsPrec with a precedence of 0.

read :: Read a => String -> a Source

The read function reads input from a string, which must be completely consumed by the input process. read fails with an error if the parse is unsuccessful, and it is therefore discouraged from being used in real applications. Use readMaybe or readEither for safe alternatives.

>>> read "123" :: Int
123

>>> read "hello" :: Int
*** Exception: Prelude.read: no parse

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

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

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

lex :: ReadS String Source

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

New parsing functions

module Text.ParserCombinators.ReadPrec

data Lexeme Source

Constructors

Char Char	Character literal
String String	String literal, with escapes interpreted
Punc String	Punctuation or reserved symbol, e.g. `(`, `::`
Ident String	Haskell identifier, e.g. `foo`, `Baz`
Symbol String	Haskell symbol, e.g. `>>`, `:%`
Number Number	Since: base-4.6.0.0
EOF

Instances

Instances details

Eq Lexeme Source	Since: base-2.1
Instance details Defined in GHC.Internal.Text.Read.Lex Methods (==) :: Lexeme -> Lexeme -> Bool Source (/=) :: Lexeme -> Lexeme -> Bool Source
Read Lexeme Source	Since: base-2.1
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Lexeme Source readList :: ReadS [Lexeme] Source readPrec :: ReadPrec Lexeme Source readListPrec :: ReadPrec [Lexeme] Source
Show Lexeme Source	Since: base-2.1
Instance details Defined in GHC.Internal.Text.Read.Lex Methods showsPrec :: Int -> Lexeme -> ShowS Source show :: Lexeme -> String Source showList :: [Lexeme] -> ShowS Source

lexP :: ReadPrec Lexeme Source

Parse a single lexeme

parens :: ReadPrec a -> ReadPrec a Source

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

readListDefault :: Read a => ReadS [a] Source

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] Source

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

readEither :: Read a => String -> Either String a Source

Parse a string using the Read instance. Succeeds if there is exactly one valid result. A Left value indicates a parse error.

>>> readEither "123" :: Either String Int
Right 123

>>> readEither "hello" :: Either String Int
Left "Prelude.read: no parse"

Since: base-4.6.0.0

readMaybe :: Read a => String -> Maybe a Source

Parse a string using the Read instance. Succeeds if there is exactly one valid result.

>>> readMaybe "123" :: Maybe Int
Just 123

>>> readMaybe "hello" :: Maybe Int
Nothing

Since: base-4.6.0.0

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/9.14.1/docs/libraries/base-4.22.0.0-66f8/Text-Read.html

Text.Read

Contents

Description

The Read class

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