Scalars

The typical scalar types String, Number, and Symbol behave as expected for describing simple datatypes.

(et-is? 4 Number)
;; -> t
(et-is? "foo" String)
;; -> t
(et-is? 'bar Symbol)
;; -> t

The numeric types Integer, Positive, and Negative exist as subtypes of Number.

(et-is? 4 Integer)
;; -> t
(et-is? 4.0 Integer)
;; -> nil
(et-is? 4.5 Integer)
;; -> nil
(et-is? 1 Positive)
;; -> t
(et-is? -1 Negative)
;; -> t
(et-is? 0 Positive)
;; -> t
(et-is? 0 Negative)
;; -> t

The types NonNilSymbol (all symbols except nil) and Var (all symbols except nil and t) exist as subtypes of Symbol.

(et-is? nil NonNilSymbol)
;; -> nil
(et-is? nil Var)
;; -> nil
(et-is? t Var)
;; -> nil

There are also a host of types representing internal emacs objects, such as Buffer, Window, Frame, Overlay, etc.

(et-is? (current-buffer) Buffer)
;; -> t
(et-is? (selected-window) Window)
;; -> t
(et-is? (selected-frame) Frame)
;; -> t

The Any type matches any value, and the NonNil type matches any value except for nil.

(et-is? 123 NonNil)
;; -> t
(et-is? 'foo NonNil)
;; -> t
(et-is? (current-buffer) NonNil)
;; -> t
(et-is? nil NonNil)
;; -> nil
(et-is? nil Any)
;; -> t