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boundp

boundp Function

Syntax:

boundp symbol → generalized-boolean

Arguments and Values:

symbol—a symbol.

generalized-boolean—a generalized boolean.

Description:

Returns true if symbol is bound; otherwise, returns false.

Examples:

(setq x 1) → 1 
(boundp ’x) → true 
(makunbound ’x) → X 
(boundp ’x) → false 
(let ((x 2)) (boundp ’x)) → false 
(let ((x 2)) (declare (special x)) (boundp ’x)) → true

Exceptional Situations:

Should signal an error of type type-error if symbol is not a symbol.

See Also:

set, setq, symbol-value, makunbound

Notes:

The function bound determines only whether a symbol has a value in the global environment; any lexical bindings are ignored.

Expanded Reference: boundp​

Basic usage​

boundp returns true if the symbol has a global (dynamic) value, and false otherwise.

(defvar *my-var* 42)
(boundp '*my-var*)
=> T

(boundp (gensym))
=> NIL

After makunbound​

makunbound removes the value binding, so boundp returns false afterwards.

(setf (symbol-value 'temp-var) 100)
(boundp 'temp-var)
=> T

(makunbound 'temp-var)
(boundp 'temp-var)
=> NIL

boundp does not see lexical bindings​

boundp only checks the global/dynamic environment, not lexical bindings.

(makunbound 'lex-test)

(let ((lex-test 99))
  (boundp 'lex-test))
=> NIL

boundp sees dynamic (special) bindings​

When a variable is declared special, boundp can see its dynamic binding.

(makunbound 'dyn-test)

(let ((dyn-test 99))
  (declare (special dyn-test))
  (boundp 'dyn-test))
=> T

Safe value access pattern​

boundp is commonly used to safely access a symbol's value without risking an error.

(defun safe-value (sym &optional default)
  (if (boundp sym)
      (symbol-value sym)
      default))

(setf (symbol-value 'configured) :yes)
(safe-value 'configured)
=> :YES
(safe-value (gensym) :not-set)
=> :NOT-SET

Keywords and constants are always bound​

(boundp :any-keyword)
=> T
(boundp t)
=> T
(boundp nil)
=> T
(boundp 'pi)
=> T