< package:mixed-types-num

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version. Using ApplicativeDo: 'a <$ bs' can be understood as the do expression

do bs
pure a

with an inferred Functor constraint.

An infix synonym for fmap. The name of this operator is an allusion to $. Note the similarities between their types:

($)  ::              (a -> b) ->   a ->   b
(<$>) :: Functor f => (a -> b) -> f a -> f b

Whereas $ is function application, <$> is function application lifted over a Functor.

Examples

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> Nothing
Nothing

>>> show <$> Just 3
Just "3"

Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17
Left 17

>>> show <$> Right 17
Right "17"

Double each element of a list:

>>> (*2) <$> [1,2,3]
[2,4,6]

Apply even to the second element of a pair:

>>> even <$> (2,2)
(2,True)

Sequence actions, discarding the value of the second argument. Using ApplicativeDo: 'as <* bs' can be understood as the do expression

do a <- as
bs
pure a

Sequential application. A few functors support an implementation of <*> that is more efficient than the default one. Using ApplicativeDo: 'fs <*> as' can be understood as the do expression

do f <- fs
a <- as
pure (f a)

An associative operation.

>>> [1,2,3] <> [4,5,6]
[1,2,3,4,5,6]

Same as >>=, but with the arguments interchanged.