$ -base -parsec
the deep analogue of $!. In the expression f $!! x, x is fully evaluated before the function f is applied to it.
Above, except that if the last line of the first argument stops at least one position before the first line of the second begins, these two lines are overlapped. For example:
> text "hi" $$ nest 5 (text "there")
lays out as
> hi there
$$ is associative, with identity empty, and also satisfies
* (x $$ y) <> z = x $$ (y <> z), if y non-empty.
Above; if there is no overlap it "dovetails" the two
Above, with no overlapping. $+$ is associative, with identity empty.
Above, without dovetailing.
Sequential function application. The argument is evaluated using the given strategy before it is given to the function.
Parallel function application. The argument is evaluated using the given strategy, in parallel with the function application.