!!
=/ a=(unit @) ~ (fall a 7)

empty, so the default wins.

glossary

=/ pins a named value (a face) into the subject for the lines below it.

name=value optionally declares the type.

=/(a 3 (add a a)) is 6.

unit is the maybe type: either ~ or [~ value].

(unit @) holds an atom or nothing.

%: 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)

fall unwraps a unit, or gives a default on ~.

(fall ~ 7) is 7.