^+ casts a value to the type of another expression, rather than a written-out type.

^+(7 42) is 42, typed like 7.

%: calls a gate with several arguments, gathering them into one sample.

%:(add 2 3) is 5.

irregular forms:

(gate a b c) is %:(gate a b c)

cat joins two atoms at a block boundary.

(cat 3 a b) concatenates by bytes.

(cat 3 'ab' 'cd') cast to @t is 'abcd'.