| Safe Haskell | Safe |
|---|---|
| Language | Haskell98 |
NumericPrelude.Base
Description
The only point of this module is to reexport items that we want from the standard Prelude.
- (!!) :: [a] -> Int -> a
- ($) :: (a -> b) -> a -> b
- ($!) :: (a -> b) -> a -> b
- (&&) :: Bool -> Bool -> Bool
- (++) :: [a] -> [a] -> [a]
- (.) :: (b -> c) -> (a -> b) -> a -> c
- (=<<) :: Monad m => (a -> m b) -> m a -> m b
- data Bool :: *
- class Bounded a where
- data Char :: *
- data Either a b :: * -> * -> *
- class Enum a where
- class Eq a where
- type FilePath = String
- class Functor (f :: * -> *) where
- data IO a :: * -> *
- type IOError = IOException
- data Maybe a :: * -> *
- class Applicative m => Monad (m :: * -> *) where
- class Eq a => Ord a where
- data Ordering :: *
- class Read a where
- type ReadS a = String -> [(a, String)]
- class Show a where
- type ShowS = String -> String
- type String = [Char]
- all :: Foldable t => (a -> Bool) -> t a -> Bool
- and :: Foldable t => t Bool -> Bool
- any :: Foldable t => (a -> Bool) -> t a -> Bool
- appendFile :: FilePath -> String -> IO ()
- asTypeOf :: a -> a -> a
- break :: (a -> Bool) -> [a] -> ([a], [a])
- concat :: Foldable t => t [a] -> [a]
- concatMap :: Foldable t => (a -> [b]) -> t a -> [b]
- const :: a -> b -> a
- curry :: ((a, b) -> c) -> a -> b -> c
- cycle :: [a] -> [a]
- drop :: Int -> [a] -> [a]
- dropWhile :: (a -> Bool) -> [a] -> [a]
- either :: (a -> c) -> (b -> c) -> Either a b -> c
- elem :: Foldable t => forall a. Eq a => a -> t a -> Bool
- error :: HasCallStack => [Char] -> a
- filter :: (a -> Bool) -> [a] -> [a]
- flip :: (a -> b -> c) -> b -> a -> c
- foldl :: Foldable t => forall b a. (b -> a -> b) -> b -> t a -> b
- foldl1 :: Foldable t => forall a. (a -> a -> a) -> t a -> a
- foldr :: Foldable t => forall a b. (a -> b -> b) -> b -> t a -> b
- foldr1 :: Foldable t => forall a. (a -> a -> a) -> t a -> a
- fst :: (a, b) -> a
- getChar :: IO Char
- getContents :: IO String
- getLine :: IO String
- head :: [a] -> a
- id :: a -> a
- init :: [a] -> [a]
- interact :: (String -> String) -> IO ()
- ioError :: IOError -> IO a
- iterate :: (a -> a) -> a -> [a]
- last :: [a] -> a
- length :: Foldable t => forall a. t a -> Int
- lex :: ReadS String
- lines :: String -> [String]
- lookup :: Eq a => a -> [(a, b)] -> Maybe b
- map :: (a -> b) -> [a] -> [b]
- mapM :: Traversable t => forall (m :: * -> *) a b. Monad m => (a -> m b) -> t a -> m (t b)
- mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()
- maximum :: Foldable t => forall a. Ord a => t a -> a
- maybe :: b -> (a -> b) -> Maybe a -> b
- minimum :: Foldable t => forall a. Ord a => t a -> a
- not :: Bool -> Bool
- notElem :: (Foldable t, Eq a) => a -> t a -> Bool
- null :: Foldable t => forall a. t a -> Bool
- or :: Foldable t => t Bool -> Bool
- otherwise :: Bool
- print :: Show a => a -> IO ()
- putChar :: Char -> IO ()
- putStr :: String -> IO ()
- putStrLn :: String -> IO ()
- read :: Read a => String -> a
- readFile :: FilePath -> IO String
- readIO :: Read a => String -> IO a
- readLn :: Read a => IO a
- readParen :: Bool -> ReadS a -> ReadS a
- reads :: Read a => ReadS a
- realToFrac :: (Real a, Fractional b) => a -> b
- repeat :: a -> [a]
- replicate :: Int -> a -> [a]
- reverse :: [a] -> [a]
- scanl :: (b -> a -> b) -> b -> [a] -> [b]
- scanl1 :: (a -> a -> a) -> [a] -> [a]
- scanr :: (a -> b -> b) -> b -> [a] -> [b]
- scanr1 :: (a -> a -> a) -> [a] -> [a]
- seq :: a -> b -> b
- sequence :: Traversable t => forall (m :: * -> *) a. Monad m => t (m a) -> m (t a)
- sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()
- showChar :: Char -> ShowS
- showParen :: Bool -> ShowS -> ShowS
- showString :: String -> ShowS
- shows :: Show a => a -> ShowS
- snd :: (a, b) -> b
- span :: (a -> Bool) -> [a] -> ([a], [a])
- splitAt :: Int -> [a] -> ([a], [a])
- tail :: [a] -> [a]
- take :: Int -> [a] -> [a]
- takeWhile :: (a -> Bool) -> [a] -> [a]
- uncurry :: (a -> b -> c) -> (a, b) -> c
- undefined :: HasCallStack => a
- unlines :: [String] -> String
- until :: (a -> Bool) -> (a -> a) -> a -> a
- unwords :: [String] -> String
- unzip :: [(a, b)] -> ([a], [b])
- unzip3 :: [(a, b, c)] -> ([a], [b], [c])
- userError :: String -> IOError
- words :: String -> [String]
- writeFile :: FilePath -> String -> IO ()
- zip :: [a] -> [b] -> [(a, b)]
- zip3 :: [a] -> [b] -> [c] -> [(a, b, c)]
- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
- zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
- (||) :: Bool -> Bool -> Bool
- catch :: IO a -> (IOError -> IO a) -> IO a
- ifThenElse :: Bool -> a -> a -> a
Documentation
(!!) :: [a] -> Int -> a infixl 9 #
List index (subscript) operator, starting from 0.
It is an instance of the more general genericIndex,
which takes an index of any integral type.
($) :: (a -> b) -> a -> b infixr 0 #
Application operator. This operator is redundant, since ordinary
application (f x) means the same as (f . However, $ x)$ has
low, right-associative binding precedence, so it sometimes allows
parentheses to be omitted; for example:
f $ g $ h x = f (g (h x))
It is also useful in higher-order situations, such as map ($ 0) xszipWith ($) fs xs
($!) :: (a -> b) -> a -> b infixr 0 #
Strict (call-by-value) application operator. It takes a function and an argument, evaluates the argument to weak head normal form (WHNF), then calls the function with that value.
(++) :: [a] -> [a] -> [a] infixr 5 #
Append two lists, i.e.,
[x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn] [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
If the first list is not finite, the result is the first list.
(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 #
Same as >>=, but with the arguments interchanged.
Instances
| Bounded Bool | Since: 2.1 |
| Enum Bool | Since: 2.1 |
| Eq Bool | |
| Ord Bool | |
| Read Bool | Since: 2.1 |
| Show Bool | |
| Ix Bool | Since: 2.1 |
| Generic Bool | |
| Lift Bool | |
| Testable Bool | |
| Arbitrary Bool | |
| CoArbitrary Bool | |
| SingKind Bool | Since: 4.9.0.0 |
| Storable Bool | Since: 2.1 |
| NFData Bool | |
| Random Bool | |
| C Bool Source # | |
| SingI Bool False | Since: 4.9.0.0 |
| SingI Bool True | Since: 4.9.0.0 |
| type Rep Bool | |
| data Sing Bool | |
| type DemoteRep Bool | |
| type (==) Bool a b | |
The Bounded class is used to name the upper and lower limits of a
type. Ord is not a superclass of Bounded since types that are not
totally ordered may also have upper and lower bounds.
The Bounded class may be derived for any enumeration type;
minBound is the first constructor listed in the data declaration
and maxBound is the last.
Bounded may also be derived for single-constructor datatypes whose
constituent types are in Bounded.
Instances
The character type Char is an enumeration whose values represent
Unicode (or equivalently ISO/IEC 10646) characters (see
http://www.unicode.org/ for details). This set extends the ISO 8859-1
(Latin-1) character set (the first 256 characters), which is itself an extension
of the ASCII character set (the first 128 characters). A character literal in
Haskell has type Char.
To convert a Char to or from the corresponding Int value defined
by Unicode, use toEnum and fromEnum from the
Enum class respectively (or equivalently ord and chr).
Instances
| Bounded Char | Since: 2.1 |
| Enum Char | Since: 2.1 |
| Eq Char | |
| Ord Char | |
| Read Char | Since: 2.1 |
| Show Char | Since: 2.1 |
| Ix Char | Since: 2.1 |
| Lift Char | |
| Arbitrary Char | |
| CoArbitrary Char | |
| Storable Char | Since: 2.1 |
| NFData Char | |
| Random Char | |
| ErrorList Char | |
| Monad m => Stream ByteString m Char | |
| Monad m => Stream ByteString m Char | |
| Monad m => Stream Text m Char | |
| Monad m => Stream Text m Char | |
| Generic1 k (URec k Char) | |
| IsString (Seq Char) | |
| Functor (URec * Char) | |
| Foldable (URec * Char) | |
| Traversable (URec * Char) | |
| Eq (URec k Char p) | |
| Ord (URec k Char p) | |
| Show (URec k Char p) | |
| Generic (URec k Char p) | |
| data URec k Char | Used for marking occurrences of Since: 4.9.0.0 |
| type Rep1 k (URec k Char) | |
| type Rep (URec k Char p) | |
data Either a b :: * -> * -> * #
The Either type represents values with two possibilities: a value of
type Either a bLeft aRight b
The Either type is sometimes used to represent a value which is
either correct or an error; by convention, the Left constructor is
used to hold an error value and the Right constructor is used to
hold a correct value (mnemonic: "right" also means "correct").
Examples
The type Either String IntString or an Int. The Left constructor can be used only on
Strings, and the Right constructor can be used only on Ints:
>>>let s = Left "foo" :: Either String Int>>>sLeft "foo">>>let n = Right 3 :: Either String Int>>>nRight 3>>>:type ss :: Either String Int>>>:type nn :: Either String Int
The fmap from our Functor instance will ignore Left values, but
will apply the supplied function to values contained in a Right:
>>>let s = Left "foo" :: Either String Int>>>let n = Right 3 :: Either String Int>>>fmap (*2) sLeft "foo">>>fmap (*2) nRight 6
The Monad instance for Either allows us to chain together multiple
actions which may fail, and fail overall if any of the individual
steps failed. First we'll write a function that can either parse an
Int from a Char, or fail.
>>>import Data.Char ( digitToInt, isDigit )>>>:{let parseEither :: Char -> Either String Int parseEither c | isDigit c = Right (digitToInt c) | otherwise = Left "parse error">>>:}
The following should work, since both '1' and '2' can be
parsed as Ints.
>>>:{let parseMultiple :: Either String Int parseMultiple = do x <- parseEither '1' y <- parseEither '2' return (x + y)>>>:}
>>>parseMultipleRight 3
But the following should fail overall, since the first operation where
we attempt to parse 'm' as an Int will fail:
>>>:{let parseMultiple :: Either String Int parseMultiple = do x <- parseEither 'm' y <- parseEither '2' return (x + y)>>>:}
>>>parseMultipleLeft "parse error"
Instances
| Arbitrary2 Either | |
| Eq2 Either | Since: 4.9.0.0 |
| Ord2 Either | Since: 4.9.0.0 |
| Read2 Either | Since: 4.9.0.0 |
| Show2 Either | Since: 4.9.0.0 |
| NFData2 Either | Since: 1.4.3.0 |
| Monad (Either e) | Since: 4.4.0.0 |
| Functor (Either a) | Since: 3.0 |
| Applicative (Either e) | Since: 3.0 |
| Foldable (Either a) | Since: 4.7.0.0 |
| Traversable (Either a) | Since: 4.7.0.0 |
| Arbitrary a => Arbitrary1 (Either a) | |
| Eq a => Eq1 (Either a) | Since: 4.9.0.0 |
| Ord a => Ord1 (Either a) | Since: 4.9.0.0 |
| Read a => Read1 (Either a) | Since: 4.9.0.0 |
| Show a => Show1 (Either a) | Since: 4.9.0.0 |
| NFData a => NFData1 (Either a) | Since: 1.4.3.0 |
| Generic1 * (Either a) | |
| (Eq b, Eq a) => Eq (Either a b) | |
| (Ord b, Ord a) => Ord (Either a b) | |
| (Read b, Read a) => Read (Either a b) | |
| (Show b, Show a) => Show (Either a b) | |
| Generic (Either a b) | |
| Semigroup (Either a b) | Since: 4.9.0.0 |
| (Lift a, Lift b) => Lift (Either a b) | |
| (Arbitrary a, Arbitrary b) => Arbitrary (Either a b) | |
| (CoArbitrary a, CoArbitrary b) => CoArbitrary (Either a b) | |
| (NFData a, NFData b) => NFData (Either a b) | |
| type Rep1 * (Either a) | |
| type Rep (Either a b) | |
| type (==) (Either k1 k2) a b | |
Class Enum defines operations on sequentially ordered types.
The enumFrom... methods are used in Haskell's translation of
arithmetic sequences.
Instances of Enum may be derived for any enumeration type (types
whose constructors have no fields). The nullary constructors are
assumed to be numbered left-to-right by fromEnum from 0 through n-1.
See Chapter 10 of the Haskell Report for more details.
For any type that is an instance of class Bounded as well as Enum,
the following should hold:
- The calls
succmaxBoundpredminBound fromEnumandtoEnumshould give a runtime error if the result value is not representable in the result type. For example,toEnum7 ::BoolenumFromandenumFromThenshould be defined with an implicit bound, thus:
enumFrom x = enumFromTo x maxBound
enumFromThen x y = enumFromThenTo x y bound
where
bound | fromEnum y >= fromEnum x = maxBound
| otherwise = minBoundMethods
the successor of a value. For numeric types, succ adds 1.
the predecessor of a value. For numeric types, pred subtracts 1.
Convert from an Int.
Convert to an Int.
It is implementation-dependent what fromEnum returns when
applied to a value that is too large to fit in an Int.
Used in Haskell's translation of [n..].
enumFromThen :: a -> a -> [a] #
Used in Haskell's translation of [n,n'..].
enumFromTo :: a -> a -> [a] #
Used in Haskell's translation of [n..m].
enumFromThenTo :: a -> a -> a -> [a] #
Used in Haskell's translation of [n,n'..m].
Instances
The Eq class defines equality (==) and inequality (/=).
All the basic datatypes exported by the Prelude are instances of Eq,
and Eq may be derived for any datatype whose constituents are also
instances of Eq.
Instances
| Eq Bool | |
| Eq Char | |
| Eq Double | |
| Eq Float | |
| Eq Int | |
| Eq Int8 | Since: 2.1 |
| Eq Int16 | Since: 2.1 |
| Eq Int32 | Since: 2.1 |
| Eq Int64 | Since: 2.1 |
| Eq Integer | |
| Eq Natural | |
| Eq Ordering | |
| Eq Word | |
| Eq Word8 | Since: 2.1 |
| Eq Word16 | Since: 2.1 |
| Eq Word32 | Since: 2.1 |
| Eq Word64 | Since: 2.1 |
| Eq SomeTypeRep | |
| Eq Exp | |
| Eq Match | |
| Eq Clause | |
| Eq Pat | |
| Eq Type | |
| Eq Dec | |
| Eq Name | |
| Eq FunDep | |
| Eq TyVarBndr | |
| Eq InjectivityAnn | |
| Eq Overlap | |
| Eq DerivStrategy | |
| Eq () | |
| Eq TyCon | |
| Eq Module | |
| Eq TrName | |
| Eq Version | Since: 2.1 |
| Eq BigNat | |
| Eq Void | Since: 4.8.0.0 |
| Eq SpecConstrAnnotation | |
| Eq Unique | |
| Eq ThreadId | Since: 4.2.0.0 |
| Eq BlockReason | |
| Eq ThreadStatus | |
| Eq AsyncException | |
| Eq ArrayException | |
| Eq ExitCode | |
| Eq IOErrorType | Since: 4.1.0.0 |
| Eq MaskingState | |
| Eq IOException | Since: 4.1.0.0 |
| Eq All | |
| Eq Any | |
| Eq Fixity | |
| Eq Associativity | |
| Eq SourceUnpackedness | |
| Eq SourceStrictness | |
| Eq DecidedStrictness | |
| Eq CChar | |
| Eq CSChar | |
| Eq CUChar | |
| Eq CShort | |
| Eq CUShort | |
| Eq CInt | |
| Eq CUInt | |
| Eq CLong | |
| Eq CULong | |
| Eq CLLong | |
| Eq CULLong | |
| Eq CBool | |
| Eq CFloat | |
| Eq CDouble | |
| Eq CPtrdiff | |
| Eq CSize | |
| Eq CWchar | |
| Eq CSigAtomic | |
| Eq CClock | |
| Eq CTime | |
| Eq CUSeconds | |
| Eq CSUSeconds | |
| Eq CIntPtr | |
| Eq CUIntPtr | |
| Eq CIntMax | |
| Eq CUIntMax | |
| Eq Fingerprint | |
| Eq Lexeme | |
| Eq Number | |
| Eq GeneralCategory | |
| Eq SrcLoc | |
| Eq IntSet | |
| Eq Extension | |
| Eq ForeignSrcLang | |
| Eq Message | |
| Eq ParseError | |
| Eq SourcePos | |
| Eq Doc | |
| Eq TextDetails | |
| Eq Style | |
| Eq Mode | |
| Eq ModName | |
| Eq PkgName | |
| Eq Module | |
| Eq OccName | |
| Eq NameFlavour | |
| Eq NameSpace | |
| Eq Loc | |
| Eq Info | |
| Eq ModuleInfo | |
| Eq Fixity | |
| Eq FixityDirection | |
| Eq Lit | |
| Eq Body | |
| Eq Guard | |
| Eq Stmt | |
| Eq Range | |
| Eq DerivClause | |
| Eq TypeFamilyHead | |
| Eq TySynEqn | |
| Eq FamFlavour | |
| Eq Foreign | |
| Eq Callconv | |
| Eq Safety | |
| Eq Pragma | |
| Eq Inline | |
| Eq RuleMatch | |
| Eq Phases | |
| Eq RuleBndr | |
| Eq AnnTarget | |
| Eq SourceUnpackedness | |
| Eq SourceStrictness | |
| Eq DecidedStrictness | |
| Eq Con | |
| Eq Bang | |
| Eq PatSynDir | |
| Eq PatSynArgs | |
| Eq FamilyResultSig | |
| Eq TyLit | |
| Eq Role | |
| Eq AnnLookup | |
| Eq LocalTime | |
| Eq TimeOfDay | |
| Eq TimeZone | |
| Eq UniversalTime | |
| Eq UTCTime | |
| Eq Day | |
| Eq T # | |
| Eq T # | |
| Eq T # | |
| Eq T # | |
| Eq Dimension # | |
| Eq a => Eq [a] | |
| Eq a => Eq (Maybe a) | |
| Eq a => Eq (Ratio a) | |
| Eq (StablePtr a) | Since: 2.1 |
| Eq (Ptr a) | |
| Eq (FunPtr a) | |
| Eq p => Eq (Par1 p) | |
| Eq a => Eq (Bounds a) | |
| Eq a => Eq (Complex a) | |
| Eq (Fixed a) | |
| Eq a => Eq (Min a) | |
| Eq a => Eq (Max a) | |
| Eq a => Eq (First a) | |
| Eq a => Eq (Last a) | |
| Eq m => Eq (WrappedMonoid m) | |
| Eq a => Eq (Option a) | |
| Eq a => Eq (NonEmpty a) | |
| Eq (StableName a) | Since: 2.1 |
| Eq a => Eq (ZipList a) | |
| Eq a => Eq (Identity a) | |
| Eq (TVar a) | Since: 4.8.0.0 |
| Eq (IORef a) | Since: 4.1.0.0 |
| Eq a => Eq (Dual a) | |
| Eq a => Eq (Sum a) | |
| Eq a => Eq (Product a) | |
| Eq a => Eq (First a) | |
| Eq a => Eq (Last a) | |
| Eq a => Eq (Down a) | |
| Eq (MVar a) | Since: 4.1.0.0 |
| Eq a => Eq (IntMap a) | |
| Eq a => Eq (Tree a) | |
| Eq a => Eq (Seq a) | |
| Eq a => Eq (ViewL a) | |
| Eq a => Eq (ViewR a) | |
| Eq a => Eq (Set a) | |
| Eq a => Eq (T a) | |
| C a => Eq (T a) | |
| Eq (Doc a) | |
| Eq a => Eq (AnnotDetails a) | |
| Eq a => Eq (Span a) | |
| Eq a => Eq (ToOrd a) # | |
| Eq a => Eq (Max a) # | |
| Eq a => Eq (Min a) # | |
| Eq a => Eq (LCM a) # | |
| Eq a => Eq (GCD a) # | |
| Eq a => Eq (T a) # | |
| Eq a => Eq (T a) # | |
| (Eq a, C a, C a) => Eq (T a) # | |
| Eq (T a) # | |
| Eq a => Eq (T a) # | |
| Eq a => Eq (Valuable a) # | |
| Eq a => Eq (T a) # | |
| C a => Eq (T a) # | |
| (Eq a, C a) => Eq (T a) # | |
| (Eq a, C a) => Eq (T a) # | |
| (Eq a, C a) => Eq (T a) # | |
| (Eq a, C a) => Eq (T a) # | |
| Ix i => Eq (T i) # | These instances may need more work They involve converting a permutation to a table. |
| Eq i => Eq (Cycle i) # | |
| Eq a => Eq (T a) # | |
| Eq a => Eq (T a) # | |
| Eq a => Eq (T a) # | |
| Eq a => Eq (T a) # | |
| (Eq a, C a) => Eq (T a) # | |
| Eq a => Eq (T a) # | |
| (Eq b, Eq a) => Eq (Either a b) | |
| Eq (V1 k p) | |
| Eq (U1 k p) | Since: 4.9.0.0 |
| Eq (TypeRep k a) | Since: 2.1 |
| (Eq a, Eq b) => Eq (a, b) | |
| (Ix i, Eq e) => Eq (Array i e) | Since: 2.1 |
| Eq a => Eq (Arg a b) | Since: 4.9.0.0 |
| Eq (Proxy k s) | Since: 4.7.0.0 |
| Eq (STRef s a) | Since: 2.1 |
| (Eq k, Eq a) => Eq (Map k a) | |
| (Eq b, Eq a) => Eq (T a b) # | |
| Eq v => Eq (T a v) # | |
| Eq a => Eq (T u a) # | |
| (Eq i, Eq a) => Eq (T i a) # | |
| Eq v => Eq (T a v) # | |
| Eq (f p) => Eq (Rec1 k f p) | |
| Eq (URec k (Ptr ()) p) | |
| Eq (URec k Char p) | |
| Eq (URec k Double p) | |
| Eq (URec k Float p) | |
| Eq (URec k Int p) | |
| Eq (URec k Word p) | |
| (Eq a, Eq b, Eq c) => Eq (a, b, c) | |
| Eq (STArray s i e) | Since: 2.1 |
| Eq a => Eq (Const k a b) | |
| Eq (f a) => Eq (Alt k f a) | |
| Eq ((:~:) k a b) | |
| (Eq e, Eq1 m, Eq a) => Eq (ErrorT e m a) | |
| Eq a => Eq (Constant k a b) | |
| Eq c => Eq (K1 k i c p) | |
| (Eq (g p), Eq (f p)) => Eq ((:+:) k f g p) | |
| (Eq (g p), Eq (f p)) => Eq ((:*:) k f g p) | |
| (Eq a, Eq b, Eq c, Eq d) => Eq (a, b, c, d) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Product * f g a) | Since: 4.9.0.0 |
| (Eq1 f, Eq1 g, Eq a) => Eq (Sum * f g a) | Since: 4.9.0.0 |
| Eq ((:~~:) k1 k2 a b) | Since: 4.10.0.0 |
| Eq (f p) => Eq (M1 k i c f p) | |
| Eq (f (g p)) => Eq ((:.:) k2 k1 f g p) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e) => Eq (a, b, c, d, e) | |
| (Eq1 f, Eq1 g, Eq a) => Eq (Compose * * f g a) | Since: 4.9.0.0 |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f) => Eq (a, b, c, d, e, f) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g) => Eq (a, b, c, d, e, f, g) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h) => Eq (a, b, c, d, e, f, g, h) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i) => Eq (a, b, c, d, e, f, g, h, i) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j) => Eq (a, b, c, d, e, f, g, h, i, j) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k) => Eq (a, b, c, d, e, f, g, h, i, j, k) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l) => Eq (a, b, c, d, e, f, g, h, i, j, k, l) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m, Eq n) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
| (Eq a, Eq b, Eq c, Eq d, Eq e, Eq f, Eq g, Eq h, Eq i, Eq j, Eq k, Eq l, Eq m, Eq n, Eq o) => Eq (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
File and directory names are values of type String, whose precise
meaning is operating system dependent. Files can be opened, yielding a
handle which can then be used to operate on the contents of that file.
class Functor (f :: * -> *) where #
The Functor class is used for types that can be mapped over.
Instances of Functor should satisfy the following laws:
fmap id == id fmap (f . g) == fmap f . fmap g
The instances of Functor for lists, Maybe and IO
satisfy these laws.
Minimal complete definition
Instances
A value of type IO aa.
There is really only one way to "perform" an I/O action: bind it to
Main.main in your program. When your program is run, the I/O will
be performed. It isn't possible to perform I/O from an arbitrary
function, unless that function is itself in the IO monad and called
at some point, directly or indirectly, from Main.main.
IO is a monad, so IO actions can be combined using either the do-notation
or the >> and >>= operations from the Monad class.
type IOError = IOException #
The Maybe type encapsulates an optional value. A value of type
Maybe aa (represented as Just aNothing). Using Maybe is a good way to
deal with errors or exceptional cases without resorting to drastic
measures such as error.
The Maybe type is also a monad. It is a simple kind of error
monad, where all errors are represented by Nothing. A richer
error monad can be built using the Either type.
Instances
| Monad Maybe | Since: 2.1 |
| Functor Maybe | Since: 2.1 |
| Applicative Maybe | Since: 2.1 |
| Foldable Maybe | Since: 2.1 |
| Traversable Maybe | Since: 2.1 |
| Arbitrary1 Maybe | |
| Eq1 Maybe | Since: 4.9.0.0 |
| Ord1 Maybe | Since: 4.9.0.0 |
| Read1 Maybe | Since: 4.9.0.0 |
| Show1 Maybe | Since: 4.9.0.0 |
| Alternative Maybe | Since: 2.1 |
| MonadPlus Maybe | Since: 2.1 |
| NFData1 Maybe | Since: 1.4.3.0 |
| Eq a => Eq (Maybe a) | |
| Ord a => Ord (Maybe a) | |
| Read a => Read (Maybe a) | Since: 2.1 |
| Show a => Show (Maybe a) | |
| Generic (Maybe a) | |
| Semigroup a => Semigroup (Maybe a) | Since: 4.9.0.0 |
| Monoid a => Monoid (Maybe a) | Lift a semigroup into Since: 2.1 |
| Lift a => Lift (Maybe a) | |
| Arbitrary a => Arbitrary (Maybe a) | |
| CoArbitrary a => CoArbitrary (Maybe a) | |
| SingKind a => SingKind (Maybe a) | Since: 4.9.0.0 |
| NFData a => NFData (Maybe a) | |
| Generic1 * Maybe | |
| SingI (Maybe a) (Nothing a) | Since: 4.9.0.0 |
| SingI a1 a2 => SingI (Maybe a1) (Just a1 a2) | Since: 4.9.0.0 |
| type Rep (Maybe a) | |
| data Sing (Maybe a) | |
| type DemoteRep (Maybe a) | |
| type Rep1 * Maybe | |
| type (==) (Maybe k) a b | |
class Applicative m => Monad (m :: * -> *) where #
The Monad class defines the basic operations over a monad,
a concept from a branch of mathematics known as category theory.
From the perspective of a Haskell programmer, however, it is best to
think of a monad as an abstract datatype of actions.
Haskell's do expressions provide a convenient syntax for writing
monadic expressions.
Instances of Monad should satisfy the following laws:
Furthermore, the Monad and Applicative operations should relate as follows:
The above laws imply:
and that pure and (<*>) satisfy the applicative functor laws.
The instances of Monad for lists, Maybe and IO
defined in the Prelude satisfy these laws.
Minimal complete definition
Methods
(>>=) :: m a -> (a -> m b) -> m b infixl 1 #
Sequentially compose two actions, passing any value produced by the first as an argument to the second.
(>>) :: m a -> m b -> m b infixl 1 #
Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.
Inject a value into the monadic type.
Fail with a message. This operation is not part of the
mathematical definition of a monad, but is invoked on pattern-match
failure in a do expression.
As part of the MonadFail proposal (MFP), this function is moved
to its own class MonadFail (see Control.Monad.Fail for more
details). The definition here will be removed in a future
release.
Instances
| Monad [] | Since: 2.1 |
| Monad Maybe | Since: 2.1 |
| Monad IO | Since: 2.1 |
| Monad Par1 | Since: 4.9.0.0 |
| Monad Q | |
| Monad Rose | |
| Monad Gen | |
| Monad P | Since: 2.1 |
| Monad Complex | Since: 4.9.0.0 |
| Monad Min | Since: 4.9.0.0 |
| Monad Max | Since: 4.9.0.0 |
| Monad First | Since: 4.9.0.0 |
| Monad Last | Since: 4.9.0.0 |
| Monad Option | Since: 4.9.0.0 |
| Monad NonEmpty | Since: 4.9.0.0 |
| Monad Identity | Since: 4.8.0.0 |
| Monad STM | Since: 4.3.0.0 |
| Monad Dual | Since: 4.8.0.0 |
| Monad Sum | Since: 4.8.0.0 |
| Monad Product | Since: 4.8.0.0 |
| Monad First | |
| Monad Last | |
| Monad ReadPrec | Since: 2.1 |
| Monad ReadP | Since: 2.1 |
| Monad Tree | |
| Monad Seq | |
| Monad (Either e) | Since: 4.4.0.0 |
| Monad (U1 *) | Since: 4.9.0.0 |
| Monoid a => Monad ((,) a) | Since: 4.9.0.0 |
| Monad m => Monad (WrappedMonad m) | |
| ArrowApply a => Monad (ArrowMonad a) | Since: 2.1 |
| Monad (Proxy *) | Since: 4.7.0.0 |
| Monad (State s) | |
| Monad (T a) # | |
| Monad (T i) # | |
| Monad f => Monad (Rec1 * f) | Since: 4.9.0.0 |
| Monad f => Monad (Alt * f) | |
| (Applicative f, Monad f) => Monad (WhenMissing f x) | Equivalent to |
| (Monad m, Error e) => Monad (ErrorT e m) | |
| Monad ((->) LiftedRep LiftedRep r) | Since: 2.1 |
| (Monad f, Monad g) => Monad ((:*:) * f g) | Since: 4.9.0.0 |
| (Monad f, Monad g) => Monad (Product * f g) | Since: 4.9.0.0 |
| (Monad f, Applicative f) => Monad (WhenMatched f x y) | Equivalent to |
| (Applicative f, Monad f) => Monad (WhenMissing f k x) | Equivalent to |
| Monad (ParsecT s u m) | |
| Monad f => Monad (M1 * i c f) | Since: 4.9.0.0 |
| (Monad f, Applicative f) => Monad (WhenMatched f k x y) | Equivalent to |
The Ord class is used for totally ordered datatypes.
Instances of Ord can be derived for any user-defined
datatype whose constituent types are in Ord. The declared order
of the constructors in the data declaration determines the ordering
in derived Ord instances. The Ordering datatype allows a single
comparison to determine the precise ordering of two objects.
Minimal complete definition: either compare or <=.
Using compare can be more efficient for complex types.
Methods
compare :: a -> a -> Ordering #
(<) :: a -> a -> Bool infix 4 #
(<=) :: a -> a -> Bool infix 4 #
(>) :: a -> a -> Bool infix 4 #
Instances
| Ord Bool | |
| Ord Char | |
| Ord Double | |
| Ord Float | |
| Ord Int | |
| Ord Int8 | Since: 2.1 |
| Ord Int16 | Since: 2.1 |
| Ord Int32 | Since: 2.1 |
| Ord Int64 | Since: 2.1 |
| Ord Integer | |
| Ord Natural | |
| Ord Ordering | |
| Ord Word | |
| Ord Word8 | Since: 2.1 |
| Ord Word16 | Since: 2.1 |
| Ord Word32 | Since: 2.1 |
| Ord Word64 | Since: 2.1 |
| Ord SomeTypeRep | |
| Ord Exp | |
| Ord Match | |
| Ord Clause | |
| Ord Pat | |
| Ord Type | |
| Ord Dec | |
| Ord Name | |
| Ord FunDep | |
| Ord TyVarBndr | |
| Ord InjectivityAnn | |
| Ord Overlap | |
| Ord DerivStrategy | |
| Ord () | |
| Ord TyCon | |
| Ord Version | Since: 2.1 |
| Ord BigNat | |
| Ord Void | Since: 4.8.0.0 |
| Ord Unique | |
| Ord ThreadId | Since: 4.2.0.0 |
| Ord BlockReason | |
| Ord ThreadStatus | |
| Ord AsyncException | |
| Ord ArrayException | |
| Ord ExitCode | |
| Ord All | |
| Ord Any | |
| Ord Fixity | |
| Ord Associativity | |
| Ord SourceUnpackedness | |
| Ord SourceStrictness | |
| Ord DecidedStrictness | |
| Ord CChar | |
| Ord CSChar | |
| Ord CUChar | |
| Ord CShort | |
| Ord CUShort | |
| Ord CInt | |
| Ord CUInt | |
| Ord CLong | |
| Ord CULong | |
| Ord CLLong | |
| Ord CULLong | |
| Ord CBool | |
| Ord CFloat | |
| Ord CDouble | |
| Ord CPtrdiff | |
| Ord CSize | |
| Ord CWchar | |
| Ord CSigAtomic | |
| Ord CClock | |
| Ord CTime | |
| Ord CUSeconds | |
| Ord CSUSeconds | |
| Ord CIntPtr | |
| Ord CUIntPtr | |
| Ord CIntMax | |
| Ord CUIntMax | |
| Ord Fingerprint | |
| Ord GeneralCategory | |
| Ord IntSet | |
| Ord Message | |
| Ord SourcePos | |
| Ord ModName | |
| Ord PkgName | |
| Ord Module | |
| Ord OccName | |
| Ord NameFlavour | |
| Ord NameSpace | |
| Ord Loc | |
| Ord Info | |
| Ord ModuleInfo | |
| Ord Fixity | |
| Ord FixityDirection | |
| Ord Lit | |
| Ord Body | |
| Ord Guard | |
| Ord Stmt | |
| Ord Range | |
| Ord DerivClause | |
| Ord TypeFamilyHead | |
| Ord TySynEqn | |
| Ord FamFlavour | |
| Ord Foreign | |
| Ord Callconv | |
| Ord Safety | |
| Ord Pragma | |
| Ord Inline | |
| Ord RuleMatch | |
| Ord Phases | |
| Ord RuleBndr | |
| Ord AnnTarget | |
| Ord SourceUnpackedness | |
| Ord SourceStrictness | |
| Ord DecidedStrictness | |
| Ord Con | |
| Ord Bang | |
| Ord PatSynDir | |
| Ord PatSynArgs | |
| Ord FamilyResultSig | |
| Ord TyLit | |
| Ord Role | |
| Ord AnnLookup | |
| Ord LocalTime | |
| Ord TimeOfDay | |
| Ord TimeZone | |
| Ord UniversalTime | |
| Ord UTCTime | |
| Ord Day | |
| Ord T # | |
| Ord T # | |
| Ord T # | |
| Ord Dimension # | |
| Ord a => Ord [a] | |
| Ord a => Ord (Maybe a) | |
| Integral a => Ord (Ratio a) | Since: 2.0.1 |
| Ord (Ptr a) | |
| Ord (FunPtr a) | |
| Ord p => Ord (Par1 p) | |
| Ord a => Ord (Bounds a) | |
| Ord (Fixed a) | |
| Ord a => Ord (Min a) | |
| Ord a => Ord (Max a) | |
| Ord a => Ord (First a) | |
| Ord a => Ord (Last a) | |
| Ord m => Ord (WrappedMonoid m) | |
| Ord a => Ord (Option a) | |
| Ord a => Ord (NonEmpty a) | |
| Ord a => Ord (ZipList a) | |
| Ord a => Ord (Identity a) | |
| Ord a => Ord (Dual a) | |
| Ord a => Ord (Sum a) | |
| Ord a => Ord (Product a) | |
| Ord a => Ord (First a) | |
| Ord a => Ord (Last a) | |
| Ord a => Ord (Down a) | Since: 4.6.0.0 |
| Ord a => Ord (IntMap a) | |
| Ord a => Ord (Seq a) | |
| Ord a => Ord (ViewL a) | |
| Ord a => Ord (ViewR a) | |
| Ord a => Ord (Set a) | |
| Ord a => Ord (T a) | |
| C a => Ord (T a) | |
| C a => Ord (ToOrd a) # | |
| (Ord a, C a) => Ord (T a) # | |
| Ord a => Ord (T a) # | |
| Ord a => Ord (Valuable a) # | |
| Ord a => Ord (T a) # | |
| C a => Ord (T a) # | |
| (C a, Ord a) => Ord (T a) # | |
| (C a, Ord a) => Ord (T a) # | |
| (Ord a, C a) => Ord (T a) # | |
| Ix i => Ord (T i) # | |
| Ord a => Ord (T a) # | |
| Ord a => Ord (T a) # | |
| (Ord b, Ord a) => Ord (Either a b) | |
| Ord (V1 k p) | |
| Ord (U1 k p) | Since: 4.9.0.0 |
| Ord (TypeRep k a) | Since: 4.4.0.0 |
| (Ord a, Ord b) => Ord (a, b) | |
| (Ix i, Ord e) => Ord (Array i e) | Since: 2.1 |
| Ord a => Ord (Arg a b) | Since: 4.9.0.0 |
| Ord (Proxy k s) | Since: 4.7.0.0 |
| (Ord k, Ord v) => Ord (Map k v) | |
| Ord v => Ord (T a v) # | |
| Ord a => Ord (T u a) # | |
| (Ord i, Ord a) => Ord (T i a) # | |
| Ord v => Ord (T a v) # | |
| Ord (f p) => Ord (Rec1 k f p) | |
| Ord (URec k (Ptr ()) p) | |
| Ord (URec k Char p) | |
| Ord (URec k Double p) | |
| Ord (URec k Float p) | |
| Ord (URec k Int p) | |
| Ord (URec k Word p) | |
| (Ord a, Ord b, Ord c) => Ord (a, b, c) | |
| Ord a => Ord (Const k a b) | |
| Ord (f a) => Ord (Alt k f a) | |
| Ord ((:~:) k a b) | |
| (Ord e, Ord1 m, Ord a) => Ord (ErrorT e m a) | |
| Ord a => Ord (Constant k a b) | |
| Ord c => Ord (K1 k i c p) | |
| (Ord (g p), Ord (f p)) => Ord ((:+:) k f g p) | |
| (Ord (g p), Ord (f p)) => Ord ((:*:) k f g p) | |
| (Ord a, Ord b, Ord c, Ord d) => Ord (a, b, c, d) | |
| (Ord1 f, Ord1 g, Ord a) => Ord (Product * f g a) | Since: 4.9.0.0 |
| (Ord1 f, Ord1 g, Ord a) => Ord (Sum * f g a) | Since: 4.9.0.0 |
| Ord ((:~~:) k1 k2 a b) | Since: 4.10.0.0 |
| Ord (f p) => Ord (M1 k i c f p) | |
| Ord (f (g p)) => Ord ((:.:) k2 k1 f g p) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e) => Ord (a, b, c, d, e) | |
| (Ord1 f, Ord1 g, Ord a) => Ord (Compose * * f g a) | Since: 4.9.0.0 |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f) => Ord (a, b, c, d, e, f) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g) => Ord (a, b, c, d, e, f, g) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h) => Ord (a, b, c, d, e, f, g, h) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i) => Ord (a, b, c, d, e, f, g, h, i) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j) => Ord (a, b, c, d, e, f, g, h, i, j) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k) => Ord (a, b, c, d, e, f, g, h, i, j, k) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l) => Ord (a, b, c, d, e, f, g, h, i, j, k, l) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m, Ord n) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m, n) | |
| (Ord a, Ord b, Ord c, Ord d, Ord e, Ord f, Ord g, Ord h, Ord i, Ord j, Ord k, Ord l, Ord m, Ord n, Ord o) => Ord (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) | |
Instances
| Bounded Ordering | Since: 2.1 |
| Enum Ordering | Since: 2.1 |
| Eq Ordering | |
| Ord Ordering | |
| Read Ordering | Since: 2.1 |
| Show Ordering | |
| Ix Ordering | Since: 2.1 |
| Generic Ordering | |
| Semigroup Ordering | Since: 4.9.0.0 |
| Monoid Ordering | Since: 2.1 |
| Arbitrary Ordering | |
| CoArbitrary Ordering | |
| NFData Ordering | |
| type Rep Ordering | |
| type (==) Ordering a b | |
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
Readinstance 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
Readwill parse only the record-syntax form, and furthermore, the fields must be given in the same order as the original declaration. - The derived
Readinstance 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 = 5Note 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 = readListPrecDefaultWhy 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:
instanceReadT wherereadPrec= ...readListPrec=readListPrecDefault
Methods
Arguments
| :: Int | the operator precedence of the enclosing
context (a number from |
| -> 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:
That is, readsPrec parses the string produced by
showsPrec, and delivers the value that
showsPrec started with.
Instances
| Read Bool | Since: 2.1 |
| Read Char | Since: 2.1 |
| Read Double | Since: 2.1 |
| Read Float | Since: 2.1 |
| Read Int | Since: 2.1 |
| Read Int8 | Since: 2.1 |
| Read Int16 | Since: 2.1 |
| Read Int32 | Since: 2.1 |
| Read Int64 | Since: 2.1 |
| Read Integer | Since: 2.1 |
| Read Natural | Since: 4.8.0.0 |
| Read Ordering | Since: 2.1 |
| Read Word | Since: 4.5.0.0 |
| Read Word8 | Since: 2.1 |
| Read Word16 | Since: 2.1 |
| Read Word32 | Since: 2.1 |
| Read Word64 | Since: 2.1 |
| Read () | Since: 2.1 |
| Read Version | |
| Read StdGen | |
| Read QCGen | |
| Read Void | Reading a |
| Read ExitCode | |
| Read All | |
| Read Any | |
| Read Fixity | |
| Read Associativity | |
| Read SourceUnpackedness | |
| Read SourceStrictness | |
| Read DecidedStrictness | |
| Read CChar | |
| Read CSChar | |
| Read CUChar | |
| Read CShort | |
| Read CUShort | |
| Read CInt | |
| Read CUInt | |
| Read CLong | |
| Read CULong | |
| Read CLLong | |
| Read CULLong | |
| Read CBool | |
| Read CFloat | |
| Read CDouble | |
| Read CPtrdiff | |
| Read CSize | |
| Read CWchar | |
| Read CSigAtomic | |
| Read CClock | |
| Read CTime | |
| Read CUSeconds | |
| Read CSUSeconds | |
| Read CIntPtr | |
| Read CUIntPtr | |
| Read CIntMax | |
| Read CUIntMax | |
| Read Lexeme | Since: 2.1 |
| Read GeneralCategory | |
| Read IntSet | |
| Read T # | |
| Read a => Read [a] | Since: 2.1 |
| Read a => Read (Maybe a) | Since: 2.1 |
| (Integral a, Read a) => Read (Ratio a) | Since: 2.1 |
| Read p => Read (Par1 p) | |
| Read a => Read (Complex a) | |
| HasResolution a => Read (Fixed a) | Since: 4.3.0.0 |
| Read a => Read (Min a) | |
| Read a => Read (Max a) | |
| Read a => Read (First a) | |
| Read a => Read (Last a) | |
| Read m => Read (WrappedMonoid m) | |
| Read a => Read (Option a) | |
| Read a => Read (NonEmpty a) | |
| Read a => Read (ZipList a) | |
| Read a => Read (Identity a) | This instance would be equivalent to the derived instances of the
Since: 4.8.0.0 |
| Read a => Read (Dual a) | |
| Read a => Read (Sum a) | |
| Read a => Read (Product a) | |
| Read a => Read (First a) | |
| Read a => Read (Last a) | |
| Read a => Read (Down a) | |
| Read e => Read (IntMap e) | |
| Read a => Read (Tree a) | |
| Read a => Read (Seq a) | |
| Read a => Read (ViewL a) | |
| Read a => Read (ViewR a) | |
| (Read a, Ord a) => Read (Set a) | |
| (Read a, C a) => Read (T a) # | |
| Read a => Read (T a) # | |
| (Read a, C a) => Read (T a) # | |
| Read i => Read (Cycle i) # | |
| Read a => Read (T a) # | |
| Read a => Read (T a) # | |
| Read a => Read (T a) # | |
| (Read b, Read a) => Read (Either a b) | |
| Read (V1 k p) | |
| Read (U1 k p) | Since: 4.9.0.0 |
| (Read a, Read b) => Read (a, b) | Since: 2.1 |
| (Ix a, Read a, Read b) => Read (Array a b) | Since: 2.1 |
| (Read b, Read a) => Read (Arg a b) | |
| Read (Proxy k s) | Since: 4.7.0.0 |
| (Ord k, Read k, Read e) => Read (Map k e) | |
| (Read v, Ord a, C a, C a v) => Read (T a v) # | |
| Read (f p) => Read (Rec1 k f p) | |
| (Read a, Read b, Read c) => Read (a, b, c) | Since: 2.1 |
| Read a => Read (Const k a b) | This instance would be equivalent to the derived instances of the
Since: 4.8.0.0 |
| Read (f a) => Read (Alt k f a) | |
| (~) k a b => Read ((:~:) k a b) | Since: 4.7.0.0 |
| (Read e, Read1 m, Read a) => Read (ErrorT e m a) | |
| Read a => Read (Constant k a b) | |
| Read c => Read (K1 k i c p) | |
| (Read (g p), Read (f p)) => Read ((:+:) k f g p) | |
| (Read (g p), Read (f p)) => Read ((:*:) k f g p) | |
| (Read a, Read b, Read c, Read d) => Read (a, b, c, d) | Since: 2.1 |
| (Read1 f, Read1 g, Read a) => Read (Product * f g a) | Since: 4.9.0.0 |
| (Read1 f, Read1 g, Read a) => Read (Sum * f g a) | Since: 4.9.0.0 |
| (~~) k1 k2 a b => Read ((:~~:) k1 k2 a b) | Since: 4.10.0.0 |
| Read (f p) => Read (M1 k i c f p) | |
| Read (f (g p)) => Read ((:.:) k2 k1 f g p) | |
| (Read a, Read b, Read c, Read d, Read e) => Read (a, b, c, d, e) | Since: 2.1 |
| (Read1 f, Read1 g, Read a) => Read (Compose * * f g a) | Since: 4.9.0.0 |
| (Read a, Read b, Read c, Read d, Read e, Read f) => Read (a, b, c, d, e, f) | Since: 2.1 |
| (Read a, Read b, Read c, Read d, Read e, Read f, Read g) => Read (a, b, c, d, e, f, g) | Since: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
| (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: 2.1 |
Conversion of values to readable Strings.
Derived instances of Show have the following properties, which
are compatible with derived instances of Read:
- The result of
showis a syntactically correct Haskell expression containing only constants, given the fixity declarations in force at the point where the type is declared. It contains only the constructor names defined in the data type, parentheses, and spaces. When labelled constructor fields are used, braces, commas, field names, and equal signs are also used. - If the constructor is defined to be an infix operator, then
showsPrecwill produce infix applications of the constructor. - the representation will be enclosed in parentheses if the
precedence of the top-level constructor in
xis less thand(associativity is ignored). Thus, ifdis0then the result is never surrounded in parentheses; ifdis11it is always surrounded in parentheses, unless it is an atomic expression. - If the constructor is defined using record syntax, then
showwill produce the record-syntax form, with the fields given in the same order as the original declaration.
For example, given the declarations
infixr 5 :^: data Tree a = Leaf a | Tree a :^: Tree a
the derived instance of Show is equivalent to
instance (Show a) => Show (Tree a) where
showsPrec d (Leaf m) = showParen (d > app_prec) $
showString "Leaf " . showsPrec (app_prec+1) m
where app_prec = 10
showsPrec d (u :^: v) = showParen (d > up_prec) $
showsPrec (up_prec+1) u .
showString " :^: " .
showsPrec (up_prec+1) v
where up_prec = 5Note that right-associativity of :^: is ignored. For example,
show(Leaf 1 :^: Leaf 2 :^: Leaf 3)"Leaf 1 :^: (Leaf 2 :^: Leaf 3)".
Methods
Arguments
| :: Int | the operator precedence of the enclosing
context (a number from |
| -> a | the value to be converted to a |
| -> ShowS |
Convert a value to a readable String.
showsPrec should satisfy the law
showsPrec d x r ++ s == showsPrec d x (r ++ s)
Derived instances of Read and Show satisfy the following:
That is, readsPrec parses the string produced by
showsPrec, and delivers the value that showsPrec started with.
Instances
all :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether all elements of the structure satisfy the predicate.
any :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether any element of the structure satisfies the predicate.
appendFile :: FilePath -> String -> IO () #
The computation appendFile file str function appends the string str,
to the file file.
Note that writeFile and appendFile write a literal string
to a file. To write a value of any printable type, as with print,
use the show function to convert the value to a string first.
main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
break :: (a -> Bool) -> [a] -> ([a], [a]) #
break, applied to a predicate p and a list xs, returns a tuple where
first element is longest prefix (possibly empty) of xs of elements that
do not satisfy p and second element is the remainder of the list:
break (> 3) [1,2,3,4,1,2,3,4] == ([1,2,3],[4,1,2,3,4]) break (< 9) [1,2,3] == ([],[1,2,3]) break (> 9) [1,2,3] == ([1,2,3],[])
concat :: Foldable t => t [a] -> [a] #
The concatenation of all the elements of a container of lists.
concatMap :: Foldable t => (a -> [b]) -> t a -> [b] #
Map a function over all the elements of a container and concatenate the resulting lists.
const x is a unary function which evaluates to x for all inputs.
For instance,
>>>map (const 42) [0..3][42,42,42,42]
cycle ties a finite list into a circular one, or equivalently,
the infinite repetition of the original list. It is the identity
on infinite lists.
drop n xs returns the suffix of xs
after the first n elements, or [] if n > :length xs
drop 6 "Hello World!" == "World!" drop 3 [1,2,3,4,5] == [4,5] drop 3 [1,2] == [] drop 3 [] == [] drop (-1) [1,2] == [1,2] drop 0 [1,2] == [1,2]
It is an instance of the more general genericDrop,
in which n may be of any integral type.
either :: (a -> c) -> (b -> c) -> Either a b -> c #
Case analysis for the Either type.
If the value is Left aa;
if it is Right bb.
Examples
We create two values of type Either String IntLeft constructor and another using the Right constructor. Then
we apply "either" the length function (if we have a String)
or the "times-two" function (if we have an Int):
>>>let s = Left "foo" :: Either String Int>>>let n = Right 3 :: Either String Int>>>either length (*2) s3>>>either length (*2) n6
elem :: Foldable t => forall a. Eq a => a -> t a -> Bool infix 4 #
Does the element occur in the structure?
error :: HasCallStack => [Char] -> a #
error stops execution and displays an error message.
filter :: (a -> Bool) -> [a] -> [a] #
filter, applied to a predicate and a list, returns the list of
those elements that satisfy the predicate; i.e.,
filter p xs = [ x | x <- xs, p x]
flip :: (a -> b -> c) -> b -> a -> c #
flip ff.
foldl :: Foldable t => forall b a. (b -> a -> b) -> b -> t a -> b #
Left-associative fold of a structure.
In the case of lists, foldl, when applied to a binary
operator, a starting value (typically the left-identity of the operator),
and a list, reduces the list using the binary operator, from left to
right:
foldl f z [x1, x2, ..., xn] == (...((z `f` x1) `f` x2) `f`...) `f` xn
Note that to produce the outermost application of the operator the
entire input list must be traversed. This means that foldl' will
diverge if given an infinite list.
Also note that if you want an efficient left-fold, you probably want to
use foldl' instead of foldl. The reason for this is that latter does
not force the "inner" results (e.g. z in the above example)
before applying them to the operator (e.g. to f x1(). This results
in a thunk chain f x2)O(n) elements long, which then must be evaluated from
the outside-in.
For a general Foldable structure this should be semantically identical
to,
foldl f z =foldlf z .toList
foldr :: Foldable t => forall a b. (a -> b -> b) -> b -> t a -> b #
Right-associative fold of a structure.
In the case of lists, foldr, when applied to a binary operator, a
starting value (typically the right-identity of the operator), and a
list, reduces the list using the binary operator, from right to left:
foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
Note that, since the head of the resulting expression is produced by
an application of the operator to the first element of the list,
foldr can produce a terminating expression from an infinite list.
For a general Foldable structure this should be semantically identical
to,
foldr f z =foldrf z .toList
getContents :: IO String #
The getContents operation returns all user input as a single string,
which is read lazily as it is needed
(same as hGetContents stdin).
Return all the elements of a list except the last one. The list must be non-empty.
interact :: (String -> String) -> IO () #
The interact function takes a function of type String->String
as its argument. The entire input from the standard input device is
passed to this function as its argument, and the resulting string is
output on the standard output device.
iterate :: (a -> a) -> a -> [a] #
iterate f x returns an infinite list of repeated applications
of f to x:
iterate f x == [x, f x, f (f x), ...]
length :: Foldable t => forall a. t a -> Int #
Returns the size/length of a finite structure as an Int. The
default implementation is optimized for structures that are similar to
cons-lists, because there is no general way to do better.
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 "" = [("","")]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
lines breaks a string up into a list of strings at newline
characters. The resulting strings do not contain newlines.
Note that after splitting the string at newline characters, the last part of the string is considered a line even if it doesn't end with a newline. For example,
lines "" == [] lines "\n" == [""] lines "one" == ["one"] lines "one\n" == ["one"] lines "one\n\n" == ["one",""] lines "one\ntwo" == ["one","two"] lines "one\ntwo\n" == ["one","two"]
Thus lines ss.
lookup :: Eq a => a -> [(a, b)] -> Maybe b #
lookup key assocs looks up a key in an association list.
map :: (a -> b) -> [a] -> [b] #
map f xs is the list obtained by applying f to each element
of xs, i.e.,
map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn] map f [x1, x2, ...] == [f x1, f x2, ...]
mapM :: Traversable t => forall (m :: * -> *) a b. Monad m => (a -> m b) -> t a -> m (t b) #
Map each element of a structure to a monadic action, evaluate
these actions from left to right, and collect the results. For
a version that ignores the results see mapM_.
maybe :: b -> (a -> b) -> Maybe a -> b #
The maybe function takes a default value, a function, and a Maybe
value. If the Maybe value is Nothing, the function returns the
default value. Otherwise, it applies the function to the value inside
the Just and returns the result.
Examples
Basic usage:
>>>maybe False odd (Just 3)True
>>>maybe False odd NothingFalse
Read an integer from a string using readMaybe. If we succeed,
return twice the integer; that is, apply (*2) to it. If instead
we fail to parse an integer, return 0 by default:
>>>import Text.Read ( readMaybe )>>>maybe 0 (*2) (readMaybe "5")10>>>maybe 0 (*2) (readMaybe "")0
Apply show to a Maybe Int. If we have Just n, we want to show
the underlying Int n. But if we have Nothing, we return the
empty string instead of (for example) "Nothing":
>>>maybe "" show (Just 5)"5">>>maybe "" show Nothing""
null :: Foldable t => forall a. t a -> Bool #
Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
print :: Show a => a -> IO () #
The print function outputs a value of any printable type to the
standard output device.
Printable types are those that are instances of class Show; print
converts values to strings for output using the show operation and
adds a newline.
For example, a program to print the first 20 integers and their powers of 2 could be written as:
main = print ([(n, 2^n) | n <- [0..19]])
read :: Read a => String -> a #
The read function reads input from a string, which must be
completely consumed by the input process.
readFile :: FilePath -> IO String #
The readFile function reads a file and
returns the contents of the file as a string.
The file is read lazily, on demand, as with getContents.
realToFrac :: (Real a, Fractional b) => a -> b #
general coercion to fractional types
replicate :: Int -> a -> [a] #
replicate n x is a list of length n with x the value of
every element.
It is an instance of the more general genericReplicate,
in which n may be of any integral type.
The value of seq a b is bottom if a is bottom, and
otherwise equal to b. seq is usually introduced to
improve performance by avoiding unneeded laziness.
A note on evaluation order: the expression seq a b does
not guarantee that a will be evaluated before b.
The only guarantee given by seq is that the both a
and b will be evaluated before seq returns a value.
In particular, this means that b may be evaluated before
a. If you need to guarantee a specific order of evaluation,
you must use the function pseq from the "parallel" package.
sequence :: Traversable t => forall (m :: * -> *) a. Monad m => t (m a) -> m (t a) #
Evaluate each monadic action in the structure from left to
right, and collect the results. For a version that ignores the
results see sequence_.
sequence_ :: (Foldable t, Monad m) => t (m a) -> m () #
Evaluate each monadic action in the structure from left to right,
and ignore the results. For a version that doesn't ignore the
results see sequence.
As of base 4.8.0.0, sequence_ is just sequenceA_, specialized
to Monad.
utility function converting a Char to a show function that
simply prepends the character unchanged.
showString :: String -> ShowS #
utility function converting a String to a show function that
simply prepends the string unchanged.
span :: (a -> Bool) -> [a] -> ([a], [a]) #
span, applied to a predicate p and a list xs, returns a tuple where
first element is longest prefix (possibly empty) of xs of elements that
satisfy p and second element is the remainder of the list:
span (< 3) [1,2,3,4,1,2,3,4] == ([1,2],[3,4,1,2,3,4]) span (< 9) [1,2,3] == ([1,2,3],[]) span (< 0) [1,2,3] == ([],[1,2,3])
splitAt :: Int -> [a] -> ([a], [a]) #
splitAt n xs returns a tuple where first element is xs prefix of
length n and second element is the remainder of the list:
splitAt 6 "Hello World!" == ("Hello ","World!")
splitAt 3 [1,2,3,4,5] == ([1,2,3],[4,5])
splitAt 1 [1,2,3] == ([1],[2,3])
splitAt 3 [1,2,3] == ([1,2,3],[])
splitAt 4 [1,2,3] == ([1,2,3],[])
splitAt 0 [1,2,3] == ([],[1,2,3])
splitAt (-1) [1,2,3] == ([],[1,2,3])It is equivalent to ( when take n xs, drop n xs)n is not _|_
(splitAt _|_ xs = _|_).
splitAt is an instance of the more general genericSplitAt,
in which n may be of any integral type.
take n, applied to a list xs, returns the prefix of xs
of length n, or xs itself if n > :length xs
take 5 "Hello World!" == "Hello" take 3 [1,2,3,4,5] == [1,2,3] take 3 [1,2] == [1,2] take 3 [] == [] take (-1) [1,2] == [] take 0 [1,2] == []
It is an instance of the more general genericTake,
in which n may be of any integral type.
takeWhile :: (a -> Bool) -> [a] -> [a] #
takeWhile, applied to a predicate p and a list xs, returns the
longest prefix (possibly empty) of xs of elements that satisfy p:
takeWhile (< 3) [1,2,3,4,1,2,3,4] == [1,2] takeWhile (< 9) [1,2,3] == [1,2,3] takeWhile (< 0) [1,2,3] == []
uncurry :: (a -> b -> c) -> (a, b) -> c #
uncurry converts a curried function to a function on pairs.
undefined :: HasCallStack => a #
until :: (a -> Bool) -> (a -> a) -> a -> a #
until p ff until p holds.
unzip :: [(a, b)] -> ([a], [b]) #
unzip transforms a list of pairs into a list of first components
and a list of second components.
words breaks a string up into a list of words, which were delimited
by white space.
writeFile :: FilePath -> String -> IO () #
The computation writeFile file str function writes the string str,
to the file file.
ifThenElse :: Bool -> a -> a -> a #
The same as if', but the name is chosen
such that it can be used for GHC-7.0's rebindable if-then-else syntax.