( ) — Group / Literal / TrainParentheses group expressions.
(2×3)+4 ⍝ 10
(1 2)(3 4) ⍝ 2⍴(1 2)(3 4)
Separators construct nested vectors. A trailing separator makes a singleton.
(42 ⋄) ⍝ ,42
(1 2 ⋄ 3 4) ⍝ (1 2)(3 4)
Two functions form an atop: (f g)Y is f(g Y).
(- +/)1 2 3 ⍝ ¯6
Three form a fork: (f g h)Y is (f Y)g(h Y). Dyadic forks pass both arguments to each arm.
(+/÷≢)2 4 9 ⍝ 5
Longer trains group from the right. A fork’s left arm can be a constant. The right arm evaluates first.