:: a -> (a -> b) -> b -package:diagrams-lib -package:quaalude -package:lens-family-core -package:funcmp package:base-prelude
& 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
$.
>>> 5 & (+1) & show
"6"
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.