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keyword

keyword Type

Supertypes:

keyword, symbol, t

Description:

The type keyword includes all symbols interned the KEYWORD package.

Interning a symbol in the KEYWORD package has three automatic effects:

1. It causes the symbol to become bound to itself.

2. It causes the symbol to become an external symbol of the KEYWORD package.

3. It causes the symbol to become a constant variable.

See Also:

keywordp

Expanded Reference: keyword​

Keywords as a type​

The keyword type includes all symbols interned in the KEYWORD package. You can test with typep or keywordp.

(typep :test 'keyword)
=> T
(typep 'test 'keyword)
=> NIL
(typep 42 'keyword)
=> NIL

Keywords are self-evaluating constants​

Interning a symbol in the KEYWORD package automatically makes it a constant variable bound to itself.

:my-keyword
=> :MY-KEYWORD
(eq :my-keyword (symbol-value :my-keyword))
=> T
(constantp :my-keyword)
=> T

Keywords are always external symbols​

All keywords are automatically exported from the KEYWORD package.

(multiple-value-bind (sym status)
    (find-symbol "TEST" "KEYWORD")
  (values sym status))
=> :TEST
=> :EXTERNAL

Keywords are a subtype of symbol​

Keywords are symbols with special properties: they live in the KEYWORD package, are self-evaluating, and are constants.

(subtypep 'keyword 'symbol)
=> T
=> T
(symbolp :example)
=> T
(keywordp :example)
=> T

Common uses of keywords​

Keywords are commonly used as indicators in property lists, keys in keyword arguments, and as enumeration-like values.

;; As function keyword arguments
(defun describe-item (&key name color)
  (format nil "~A is ~A" name color))

(describe-item :name "apple" :color "red")
=> "apple is red"

;; As property list indicators
(let ((sym (make-symbol "ITEM")))
  (setf (get sym :type) :fruit)
  (get sym :type))
=> :FRUIT