Safe Haskell | Safe |
---|---|
Language | Haskell2010 |
Synopsis
- class Functor f => Applicative (f :: * -> *) where
- between :: Applicative m => m open -> m close -> m a -> m a
- filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]
- forever :: Applicative f => f a -> f b
- liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
- replicateM :: Applicative m => Int -> m a -> m [a]
- replicateM_ :: Applicative m => Int -> m a -> m ()
- unless :: Applicative f => Bool -> f () -> f ()
- when :: Applicative f => Bool -> f () -> f ()
- zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]
- zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()
- class Applicative f => Alternative (f :: * -> *) where
- endBy :: Alternative m => m a -> m sep -> m [a]
- endBy1 :: Alternative m => m a -> m sep -> m (NonEmpty a)
- guard :: Alternative f => Bool -> f ()
- manyTill :: Alternative m => m a -> m end -> m [a]
- optional :: (Alt f, Applicative f) => f a -> f (Maybe a)
- sepBy :: Alternative m => m a -> m sep -> m [a]
- sepEndBy :: Alternative m => m a -> m sep -> m [a]
- sepBy1 :: Alternative m => m a -> m sep -> m (NonEmpty a)
- sepEndBy1 :: Alternative m => m a -> m sep -> m (NonEmpty a)
- skipMany :: Alternative m => m a -> m ()
- skipManyTill :: Alternative m => m a -> m end -> m end
- skipSome :: Alternative m => m a -> m ()
- skipSomeTill :: Alternative m => m a -> m end -> m end
- some1 :: Alternative f => f a -> f (NonEmpty a)
- someTill :: Alternative m => m a -> m end -> m (NonEmpty a)
- newtype Alt (f :: k -> *) (a :: k) :: forall k. (k -> *) -> k -> * = Alt {
- getAlt :: f a
- data Ap (f :: * -> *) a where
- runAp :: Applicative g => (forall x. f x -> g x) -> Ap f a -> g a
- runAp_ :: Monoid m => (forall a. f a -> m) -> Ap f b -> m
- liftAp :: f a -> Ap f a
- iterAp :: Functor g => (g a -> a) -> Ap g a -> a
- hoistAp :: (forall a. f a -> g a) -> Ap f b -> Ap g b
- retractAp :: Applicative f => Ap f a -> f a
Applicative
class Functor f => Applicative (f :: * -> *) where #
A functor with application, providing operations to
A minimal complete definition must include implementations of pure
and of either <*>
or liftA2
. If it defines both, then they must behave
the same as their default definitions:
(<*>
) =liftA2
id
liftA2
f x y = f<$>
x<*>
y
Further, any definition must satisfy the following:
- identity
pure
id
<*>
v = v- composition
pure
(.)<*>
u<*>
v<*>
w = u<*>
(v<*>
w)- homomorphism
pure
f<*>
pure
x =pure
(f x)- interchange
u
<*>
pure
y =pure
($
y)<*>
u
The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:
As a consequence of these laws, the Functor
instance for f
will satisfy
It may be useful to note that supposing
forall x y. p (q x y) = f x . g y
it follows from the above that
liftA2
p (liftA2
q u v) =liftA2
f u .liftA2
g v
If f
is also a Monad
, it should satisfy
(which implies that pure
and <*>
satisfy the applicative functor laws).
Lift a value.
(<*>) :: f (a -> b) -> f a -> f b infixl 4 #
Sequential application.
A few functors support an implementation of <*>
that is more
efficient than the default one.
liftA2 :: (a -> b -> c) -> f a -> f b -> f c #
Lift a binary function to actions.
Some functors support an implementation of liftA2
that is more
efficient than the default one. In particular, if fmap
is an
expensive operation, it is likely better to use liftA2
than to
fmap
over the structure and then use <*>
.
(*>) :: f a -> f b -> f b infixl 4 #
Sequence actions, discarding the value of the first argument.
(<*) :: f a -> f b -> f a infixl 4 #
Sequence actions, discarding the value of the second argument.
Instances
between :: Applicative m => m open -> m close -> m a -> m a #
parses between
open close popen
, followed by p
and close
.
Returns the value returned by p
.
braces = between (symbol "{") (symbol "}")
filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #
This generalizes the list-based filter
function.
forever :: Applicative f => f a -> f b #
repeats the action infinitely.forever
act
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d #
Lift a ternary function to actions.
replicateM :: Applicative m => Int -> m a -> m [a] #
performs the action replicateM
n actn
times,
gathering the results.
replicateM_ :: Applicative m => Int -> m a -> m () #
Like replicateM
, but discards the result.
unless :: Applicative f => Bool -> f () -> f () #
The reverse of when
.
when :: Applicative f => Bool -> f () -> f () #
Conditional execution of Applicative
expressions. For example,
when debug (putStrLn "Debugging")
will output the string Debugging
if the Boolean value debug
is True
, and otherwise do nothing.
zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #
zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #
Alternative
class Applicative f => Alternative (f :: * -> *) where #
A monoid on applicative functors.
If defined, some
and many
should be the least solutions
of the equations:
The identity of <|>
(<|>) :: f a -> f a -> f a infixl 3 #
An associative binary operation
Zero or more.
Instances
endBy :: Alternative m => m a -> m sep -> m [a] #
parses zero or more occurrences of endBy
p sepp
, separated and
ended by sep
. Returns a list of values returned by p
.
cStatements = cStatement `endBy` semicolon
endBy1 :: Alternative m => m a -> m sep -> m (NonEmpty a) #
parses one or more occurrences of endBy1
p sepp
, separated and
ended by sep
. Returns a non-empty list of values returned by p
.
guard :: Alternative f => Bool -> f () #
Conditional failure of Alternative
computations. Defined by
guard True =pure
() guard False =empty
Examples
Common uses of guard
include conditionally signaling an error in
an error monad and conditionally rejecting the current choice in an
Alternative
-based parser.
As an example of signaling an error in the error monad Maybe
,
consider a safe division function safeDiv x y
that returns
Nothing
when the denominator y
is zero and
otherwise. For example:Just
(x `div`
y)
>>> safeDiv 4 0 Nothing >>> safeDiv 4 2 Just 2
A definition of safeDiv
using guards, but not guard
:
safeDiv :: Int -> Int -> Maybe Int safeDiv x y | y /= 0 = Just (x `div` y) | otherwise = Nothing
A definition of safeDiv
using guard
and Monad
do
-notation:
safeDiv :: Int -> Int -> Maybe Int safeDiv x y = do guard (y /= 0) return (x `div` y)
manyTill :: Alternative m => m a -> m end -> m [a] #
applies parser manyTill
p endp
zero or more times until parser
end
succeeds. Returns the list of values returned by p
.
See also: skipMany
, skipManyTill
.
optional :: (Alt f, Applicative f) => f a -> f (Maybe a) #
One or none.
sepBy :: Alternative m => m a -> m sep -> m [a] #
parses zero or more occurrences of sepBy
p sepp
, separated by
sep
. Returns a list of values returned by p
.
commaSep p = p `sepBy` comma
sepEndBy :: Alternative m => m a -> m sep -> m [a] #
parses zero or more occurrences of sepEndBy
p sepp
, separated
and optionally ended by sep
. Returns a list of values returned by p
.
sepBy1 :: Alternative m => m a -> m sep -> m (NonEmpty a) #
parses one or more occurrences of sepBy1
p sepp
, separated by
sep
. Returns a non-empty list of values returned by p
.
sepEndBy1 :: Alternative m => m a -> m sep -> m (NonEmpty a) #
parses one or more occurrences of sepEndBy1
p sepp
, separated
and optionally ended by sep
. Returns a non-empty list of values returned by
p
.
skipMany :: Alternative m => m a -> m () #
applies the parser skipMany
pp
zero or more times, skipping
its result.
See also: manyTill
, skipManyTill
.
skipManyTill :: Alternative m => m a -> m end -> m end #
applies the parser skipManyTill
p endp
zero or more times
skipping results until parser end
succeeds. Result parsed by end
is
then returned.
skipSome :: Alternative m => m a -> m () #
applies the parser skipSome
pp
one or more times, skipping its
result.
See also: someTill
, skipSomeTill
.
skipSomeTill :: Alternative m => m a -> m end -> m end #
applies the parser skipSomeTill
p endp
one or more times
skipping results until parser end
succeeds. Result parsed by end
is
then returned.
some1 :: Alternative f => f a -> f (NonEmpty a) #
sequences some1
xx
one or more times.
someTill :: Alternative m => m a -> m end -> m (NonEmpty a) #
works similarly to someTill
p end
, but manyTill
p endp
should succeed at least once.
See also: skipSome
, skipSomeTill
.
Newtypes
newtype Alt (f :: k -> *) (a :: k) :: forall k. (k -> *) -> k -> * #
Monoid under <|>
.
Since: base-4.8.0.0
Instances
Generic1 (Alt f :: k -> *) | |
Monad f => Monad (Alt f) | |
Functor f => Functor (Alt f) | |
MonadFix f => MonadFix (Alt f) | Since: base-4.8.0.0 |
Defined in Control.Monad.Fix | |
Applicative f => Applicative (Alt f) | |
Alternative f => Alternative (Alt f) | |
Contravariant f => Contravariant (Alt f) | |
MonadPlus f => MonadPlus (Alt f) | |
MonadZip f => MonadZip (Alt f) | Since: base-4.8.0.0 |
Divisible f => Divisible (Alt f) | |
Decidable f => Decidable (Alt f) | |
Apply f => Apply (Alt f) | |
Traversable1 f => Traversable1 (Alt f) | |
Foldable1 f => Foldable1 (Alt f) | |
Bind f => Bind (Alt f) | |
Extend f => Extend (Alt f) | |
Enum (f a) => Enum (Alt f a) | |
Eq (f a) => Eq (Alt f a) | |
(Data (f a), Data a, Typeable f) => Data (Alt f a) | Since: base-4.8.0.0 |
Defined in Data.Data gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Alt f a -> c (Alt f a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Alt f a) # toConstr :: Alt f a -> Constr # dataTypeOf :: Alt f a -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Alt f a)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Alt f a)) # gmapT :: (forall b. Data b => b -> b) -> Alt f a -> Alt f a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Alt f a -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Alt f a -> r # gmapQ :: (forall d. Data d => d -> u) -> Alt f a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Alt f a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Alt f a -> m (Alt f a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Alt f a -> m (Alt f a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Alt f a -> m (Alt f a) # | |
Num (f a) => Num (Alt f a) | |
Ord (f a) => Ord (Alt f a) | |
Read (f a) => Read (Alt f a) | |
Show (f a) => Show (Alt f a) | |
Generic (Alt f a) | |
Alternative f => Semigroup (Alt f a) | Since: base-4.9.0.0 |
Alternative f => Monoid (Alt f a) | Since: base-4.8.0.0 |
Wrapped (Alt f a) | |
Serialise (f a) => Serialise (Alt f a) | Since: serialise-0.2.0.0 |
t ~ Alt g b => Rewrapped (Alt f a) t | |
Defined in Control.Lens.Wrapped | |
type Rep1 (Alt f :: k -> *) | |
Defined in Data.Semigroup.Internal | |
type Rep (Alt f a) | |
Defined in Data.Semigroup.Internal | |
type Unwrapped (Alt f a) | |
Defined in Control.Lens.Wrapped |
Free applicative
data Ap (f :: * -> *) a where #
The free Applicative
for a Functor
f
.
runAp :: Applicative g => (forall x. f x -> g x) -> Ap f a -> g a #
Given a natural transformation from f
to g
, this gives a canonical monoidal natural transformation from
to Ap
fg
.
runAp t == retractApp . hoistApp t
runAp_ :: Monoid m => (forall a. f a -> m) -> Ap f b -> m #
Perform a monoidal analysis over free applicative value.
Example:
count :: Ap f a -> Int count = getSum . runAp_ (\_ -> Sum 1)
iterAp :: Functor g => (g a -> a) -> Ap g a -> a #
Tear down a free Applicative
using iteration.