* package:rebase

Split the input between the two argument arrows and combine their output. Note that this is in general not a functor. The default definition may be overridden with a more efficient version if desired.

Sequence actions, discarding the value of the first argument.

Examples

If used in conjunction with the Applicative instance for Maybe, you can chain Maybe computations, with a possible "early return" in case of Nothing.

>>> Just 2 *> Just 3
Just 3

>>> Nothing *> Just 3
Nothing

Of course a more interesting use case would be to have effectful computations instead of just returning pure values.

>>> import Data.Char

>>> import Text.ParserCombinators.ReadP

>>> let p = string "my name is " *> munch1 isAlpha <* eof

>>> readP_to_S p "my name is Simon"
[("Simon","")]

Sequence actions, discarding the value of the second argument.

A variant of <*> with the arguments reversed.

Apply a possibly-empty-with-unit container of functions to a non-empty container of values.

Sequential application. A few functors support an implementation of <*> that is more efficient than the default one.

Example

Used in combination with (<$>), (<*>) can be used to build a record.

>>> data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}

>>> produceFoo :: Applicative f => f Foo

>>> produceBar :: Applicative f => f Bar

>>> produceBaz :: Applicative f => f Baz

>>> mkState :: Applicative f => f MyState

>>> mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz

An operator alias for select, which is sometimes convenient. It tries to follow the notational convention for Applicative operators. The angle bracket pointing to the left means we always use the corresponding value. The value on the right, however, may be skipped, hence the question mark.

Apply a non-empty container of functions to a possibly-empty-with-unit container of values.