bool

A bool is either true or false.

predicate

(bool? x)

(bool? true) -> true
(bool? false) -> true
(bool? null) -> false
(bool? "true") -> false
(bool? 0) -> false

x.type -> bool

x.to-bool -> x

x.to-text -> "true" or "false"

x.view -> x

x.not -> (not x)