Documentation

& is a reverse application operator. This provides notational convenience. Its precedence is one higher than that of the forward application operator $, which allows & to be nested in $.

This is a version of flip id, where id is specialized from a -> a to (a -> b) -> (a -> b) which by the associativity of (->) is (a -> b) -> a -> b. flipping this yields a -> (a -> b) -> b which is the type signature of &

Examples

>>> 5 & (+1) & show
"6"

>>> sqrt $ [1 / n^2 | n <- [1..1000]] & sum & (*6)
3.1406380562059946

Since: base-4.8.0.0

applyWhen applies a function to a value if a condition is true, otherwise, it returns the value unchanged.

It is equivalent to flip (bool id).

Examples

>>> map (\x -> applyWhen (odd x) (*2) x) [1..10]
[2,2,6,4,10,6,14,8,18,10]

>>> map (\x -> applyWhen (length x > 6) ((++ "...") . take 3) x) ["Hi!", "This is amazing", "Hope you're doing well today!", ":D"]
["Hi!","Thi...","Hop...",":D"]

Algebraic properties

Since: base-4.18.0.0