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macro-function

macro-function Accessor

Syntax:

macro-function symbol &optional environment → function

(setf (macro-function symbol &optional environment**)** new-function**)**

Arguments and Values:

symbol—a symbol.

environment—an environment object.

function—a macro function or nil.

new-function—a macro function.

Description:

Determines whether symbol has a function definition as a macro in the specified environment.

If so, the macro expansion function, a function of two arguments, is returned. If symbol has no function definition in the lexical environment environment, or its definition is not a macro, macro-function returns nil.

It is possible for both macro-function and special-operator-p to return true of symbol. The macro definition must be available for use by programs that understand only the standard Common Lisp special forms.

Examples:

(defmacro macfun (x) ’(macro-function ’macfun)) → MACFUN 
(not (macro-function ’macfun)) → false 
(macrolet ((foo (&environment env) 
	     (if (macro-function ’bar env) 
		 ”yes 
		  ”no))) 
  (list (foo) 
	(macrolet ((bar () :beep)) 
	  (foo)))) 
→ (NO YES)

Affected By:

(setf macro-function), defmacro, and macrolet.

Exceptional Situations:

The consequences are undefined if environment is non-nil in a use of setf of macro-function.

See Also:

defmacro, Section 3.1 (Evaluation)

Notes:

setf can be used with macro-function to install a macro as a symbol’s global function definition: (setf (macro-function symbol) fn)

The value installed must be a function that accepts two arguments, the entire macro call and an environment, and computes the expansion for that call. Performing this operation causes symbol to have only that macro definition as its global function definition; any previous definition, whether as a macro or as a function, is lost.

macroexpand, macroexpand-1

Expanded Reference: macro-function​

Testing Whether a Symbol Names a Macro​

macro-function returns the macro function if the symbol has a macro definition, or nil otherwise.

(defmacro my-macro (x) `(list ,x))
=> MY-MACRO

(macro-function 'my-macro)
==> #<FUNCTION ...>

(macro-function 'car)
=> NIL

Installing a Macro Function with setf​

You can use setf of macro-function to install a macro expansion function directly. The function must accept two arguments: the form and an environment.

(setf (macro-function 'my-nop)
      (lambda (form env)
        (declare (ignore form env))
        nil))
==> #<FUNCTION ...>

(my-nop anything here)
=> NIL

Interaction with macrolet​

macro-function can detect macros in a lexical environment when used inside a macro that receives &environment.

(defmacro macro-defined-p (name &environment env)
  (if (macro-function name env)
      ''yes
      ''no))
=> MACRO-DEFINED-P

(macro-defined-p defun)
=> YES

(macrolet ((local-mac () 42))
  (macro-defined-p local-mac))
=> YES

Difference from special-operator-p​

A symbol can be both a special operator and have a macro function. macro-function and special-operator-p can both return true for the same symbol.

;; Some implementations provide macro definitions for special operators
;; as a compatibility aid. Results are implementation-dependent:
(and (special-operator-p 'setq)
     (not (null (macro-function 'setq))))
=> NIL