define-compiler-macro name lambda-list {[[{declaration}{* | documentation]]} {form}{*}}
=> name
name---a function name.
lambda-list---a macro lambda list.
declaration---a declare expression; not evaluated.
documentation---a string; not evaluated.
form---a form.
[Editorial Note by KMP: This definition probably needs to be fully expanded to not refer through the definition of defmacro, but should suffice for now.]
This is the normal mechanism for defining a compiler macro function. Its manner of definition is the same as for defmacro; the only differences are:
(defun square (x) (expt x 2)) => SQUARE
(define-compiler-macro square (&whole form arg)
(if (atom arg)
`(expt ,arg 2)
(case (car arg)
(square (if (= (length arg) 2)
`(expt ,(nth 1 arg) 4)
form))
(expt (if (= (length arg) 3)
(if (numberp (nth 2 arg))
`(expt ,(nth 1 arg) ,(* 2 (nth 2 arg)))
`(expt ,(nth 1 arg) (* 2 ,(nth 2 arg))))
form))
(otherwise `(expt ,arg 2))))) => SQUARE
(square (square 3)) => 81
(macroexpand '(square x)) => (SQUARE X), false
(funcall (compiler-macro-function 'square) '(square x) nil)
=> (EXPT X 2)
(funcall (compiler-macro-function 'square) '(square (square x)) nil)
=> (EXPT X 4)
(funcall (compiler-macro-function 'square) '(funcall #'square x) nil)
=> (EXPT X 2)
(defun distance-positional (x1 y1 x2 y2)
(sqrt (+ (expt (- x2 x1) 2) (expt (- y2 y1) 2))))
=> DISTANCE-POSITIONAL
(defun distance (&key (x1 0) (y1 0) (x2 x1) (y2 y1))
(distance-positional x1 y1 x2 y2))
=> DISTANCE
(define-compiler-macro distance (&whole form
&rest key-value-pairs
&key (x1 0 x1-p)
(y1 0 y1-p)
(x2 x1 x2-p)
(y2 y1 y2-p)
&allow-other-keys
&environment env)
(flet ((key (n) (nth (* n 2) key-value-pairs))
(arg (n) (nth (1+ (* n 2)) key-value-pairs))
(simplep (x)
(let ((expanded-x (macroexpand x env)))
(or (constantp expanded-x env)
(symbolp expanded-x)))))
(let ((n (/ (length key-value-pairs) 2)))
(multiple-value-bind (x1s y1s x2s y2s others)
(loop for (key) on key-value-pairs by #'cddr
count (eq key ':x1) into x1s
count (eq key ':y1) into y1s
count (eq key ':x2) into x2s
count (eq key ':y1) into y2s
count (not (member key '(:x1 :x2 :y1 :y2)))
into others
finally (return (values x1s y1s x2s y2s others)))
(cond ((and (= n 4)
(eq (key 0) :x1)
(eq (key 1) :y1)
(eq (key 2) :x2)
(eq (key 3) :y2))
`(distance-positional ,x1 ,y1 ,x2 ,y2))
((and (if x1-p (and (= x1s 1) (simplep x1)) t)
(if y1-p (and (= y1s 1) (simplep y1)) t)
(if x2-p (and (= x2s 1) (simplep x2)) t)
(if y2-p (and (= y2s 1) (simplep y2)) t)
(zerop others))
`(distance-positional ,x1 ,y1 ,x2 ,y2))
((and (< x1s 2) (< y1s 2) (< x2s 2) (< y2s 2)
(zerop others))
(let ((temps (loop repeat n collect (gensym))))
`(let ,(loop for i below n
collect (list (nth i temps) (arg i)))
(distance
,@(loop for i below n
append (list (key i) (nth i temps)))))))
(t form))))))
=> DISTANCE
(dolist (form
'((distance :x1 (setq x 7) :x2 (decf x) :y1 (decf x) :y2 (decf x))
(distance :x1 (setq x 7) :y1 (decf x) :x2 (decf x) :y2 (decf x))
(distance :x1 (setq x 7) :y1 (incf x))
(distance :x1 (setq x 7) :y1 (incf x) :x1 (incf x))
(distance :x1 a1 :y1 b1 :x2 a2 :y2 b2)
(distance :x1 a1 :x2 a2 :y1 b1 :y2 b2)
(distance :x1 a1 :y1 b1 :z1 c1 :x2 a2 :y2 b2 :z2 c2)))
(print (funcall (compiler-macro-function 'distance) form nil)))
|> (LET ((#:G6558 (SETQ X 7))
|> (#:G6559 (DECF X))
|> (#:G6560 (DECF X))
|> (#:G6561 (DECF X)))
|> (DISTANCE :X1 #:G6558 :X2 #:G6559 :Y1 #:G6560 :Y2 #:G6561))
|> (DISTANCE-POSITIONAL (SETQ X 7) (DECF X) (DECF X) (DECF X))
|> (LET ((#:G6567 (SETQ X 7))
|> (#:G6568 (INCF X)))
|> (DISTANCE :X1 #:G6567 :Y1 #:G6568))
|> (DISTANCE :X1 (SETQ X 7) :Y1 (INCF X) :X1 (INCF X))
|> (DISTANCE-POSITIONAL A1 B1 A2 B2)
|> (DISTANCE-POSITIONAL A1 B1 A2 B2)
|> (DISTANCE :X1 A1 :Y1 B1 :Z1 C1 :X2 A2 :Y2 B2 :Z2 C2)
=> NIL
section compiler-macro-function [Accessor] , section defmacro [Macro] , @xref{documentation; (setf documentation)} , section Syntactic Interaction of Documentation Strings and Declarations
The consequences of writing a compiler macro definition for a function in the COMMON-LISP package are undefined; it is quite possible that in some implementations such an attempt would override an equivalent or equally important definition. In general, it is recommended that a programmer only write compiler macro definitions for functions he or she personally maintains--writing a compiler macro definition for a function maintained elsewhere is normally considered a violation of traditional rules of modularity and data abstraction.
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