$ package:numeric-prelude

Application operator. This operator is redundant, since ordinary application (f x) means the same as (f $ x). However, $ 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) xs, or zipWith ($) fs xs. Note that ($) is levity-polymorphic in its result type, so that foo $ True where foo :: Bool -> Int# is well-typed.

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.

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.