我在Common Lisp中编写自己的x86-64汇编程序，它为x86-64的子集生成正确的二进制代码。我使用自定义阅读器宏将汇编代码转换为语法树，并按预期工作。
我试图完成的是允许在汇编代码中使用Lisp代码，这样我就可以使用 Lisp作为汇编语言的宏语言。我使用#a作为宏调度字符，#e为读者发出信号。内部阅读器#l更改为Lisp模式，#a更改回组装模式，#e（表示阅读器宏的信号结束）应该在两种模式下都有效。
我不明白的是如何将评估代码的结果输出回输入流（在其余代码之前处理），或者如何获取Lisp代码输出再次阅读，以便可以适当地处理Lisp代码的输出（它将是汇编代码）（与汇编代码的其余部分相同）。我怎样才能实现这一目标？
旁注：这是我的第一个读者宏，因此可能存在设计缺陷。我认为我将Lisp代码读入字符串的方法不一定是最好的方法，如果有一些更短，更惯用的方法。
这是我的阅读器宏的简化版本：
(eval-when (:compile-toplevel :load-toplevel :execute)
(defun get-last-character-string (my-string)
"This function returns a string consisting of the last character of the input string."
(subseq my-string (1- (length my-string))))
(defun get-string-without-last-character (my-string)
"This function returns a string without the last character of the input string."
(subseq my-string 0 (1- (length my-string))))
(defun get-string-without-invalid-last-character (my-string invalid-last-characters)
"If the last character of the string is invalid, the string is returned without it, otherwise completely."
(loop for invalid-last-character in invalid-last-characters
do (if (equal (get-last-character-string my-string) invalid-last-character)
(setf my-string (get-string-without-last-character my-string))))
my-string)
(defun transform-code-to-string (stream sub-char numarg)
"This function converts assembly code into a string.
#l marks change to Lisp code. #a marks return to asm. #e marks end.
Partially based on: http://weitz.de/macros.lisp"
(declare (ignore sub-char numarg))
(let*
((invalid-last-characters (list "'" " " "(" ")"))
(current-mode "asm")
(is-there-code-on-this-line nil)
(current-phase "beginning-of-line")
(my-string "(list ")
(lisp-code-string ""))
;; loop through stream.
(loop for my-char = (coerce (list (read-char stream t nil t)) 'string)
do (cond
((equal current-mode "asm")
(cond
((equal current-phase "hash-sign-read")
;; is character e ?
;; if yes, we're done, fix closing parentheses and return.
(cond
((equal my-char "e")
(return-from transform-code-to-string
(concatenate 'string (get-string-without-invalid-last-character
(get-string-without-invalid-last-character
my-string invalid-last-characters)
invalid-last-characters) "))")))
;; is character l ?
;; if yes, change to Lisp mode.
((equal my-char "l")
;; could Lisp code could be read and evaluated here
;; without reading it into a string?
(progn
(setf current-mode "Lisp")
(setf is-there-code-on-this-line nil)
(setf lisp-code-string "")
(setf current-phase "beginning-of-line")))
;; otherwise, print error.
(t (error "in asm mode undefined control character after #"))))
;; is character # ?
;; if yes, mark hash sign read.
((equal my-char "#")
(setf current-phase "hash-sign-read"))
;; is character newline?
((equal my-char (coerce (list #\Newline) 'string))
(progn
(cond
;; is there _no_ code on this line?
;; if true, do not output anything.
((not is-there-code-on-this-line)
(setf current-phase "beginning-of-line"))
;; are we inside instruction or inside a parameter?
;; if true, output ")
((or (equal current-phase "inside-instruction")
(equal current-phase "inside-parameters"))
(progn
(setf current-phase "beginning-of-line")
(setf is-there-code-on-this-line nil)
(setf my-string (concatenate 'string my-string "\")"))))
;; otherwise output )
(t (progn
(setf current-phase "beginning-of-line")
(setf is-there-code-on-this-line nil)
(setf my-string (concatenate 'string my-string ")")))))))
;; are we inside a comment?
;; if yes, don't output anything.
((equal current-phase "inside-comment")
nil)
;; are we in the beginning of the line?
((equal current-phase "beginning-of-line")
(cond
;; is this a space in the beginning of the line?
;; if yes, do not output anything.
((equal my-char " ")
nil)
;; is this the first character of instruction and not ( or ) ?
;; if yes, mark there is code on this line, mark first character as printed, output " and current character.
((and
(not (equal my-char "("))
(not (equal my-char ")")))
(progn
(setf current-phase "inside-instruction")
(setf is-there-code-on-this-line t)
(setf my-string (concatenate 'string my-string "'(\"" my-char))))
(t nil)))
;; is character ; ?
;; if yes, don't output anything, begin comment.
((equal my-char ";")
(setf current-phase "inside-comment"))
;; is character space or comma?
((or (equal my-char " ")
(equal my-char ","))
(cond
;; is character space or comma, and last character was _not_ space, comma or opening parenthesis?
;; if yes, output " and space.
((and
(not (equal (get-last-character-string my-string) " "))
(not (equal (get-last-character-string my-string) ","))
(not (equal (get-last-character-string my-string) "(")))
(progn
(setf current-phase "in-space")
(setf my-string (concatenate 'string my-string "\" "))))
(t nil)))
;; is instruction printed and this is the 1st character of a parameter?
((and
(not (equal current-phase "inside-instruction"))
(or (equal (get-last-character-string my-string) " ")
(equal (get-last-character-string my-string) ",")))
(cond
;; mark we're inside parameters, output " and current character.
(t (progn
(setf current-phase "inside-parameters")
(setf my-string (concatenate 'string my-string "\"" my-char))))))
;; otherwise output the character.
(t (setf my-string (concatenate 'string my-string my-char)))))
((equal current-mode "Lisp")
;; in Lisp mode, read text until #e or #a is reached and eval it.
(cond
((equal current-phase "hash-sign-read")
(cond
;; is character e ?
;; if yes, we're done, fix closing parentheses and return.
((equal my-char "e")
(progn
(concatenate 'string "#a" (eval lisp-code-string) "#e") ; this should be something different.
(return-from transform-code-to-string
(concatenate 'string (get-string-without-invalid-last-character
(get-string-without-invalid-last-character
my-string invalid-last-characters)
invalid-last-characters) "))"))))
;; is character a ?
;; if yes, change to asm mode.
((equal my-char "a")
(progn
(setf current-mode "asm")
(setf is-there-code-on-this-line nil)
(setf current-phase "beginning-of-line")
(concatenate 'string "#a" (eval lisp-code-string) "#e") ; this should be something different.
;; otherwise, add # and the character to the Lisp code to be evaluated.
(t (progn
(setf current-phase "")
(setf my-string (concatenate 'string lisp-code-string "#" my-char))))))
;; is character # ?
;; if yes, mark hash sign read.
((equal my-char "#")
(setf current-phase "hash-sign-read"))
;; otherwise add the character to the Lisp code to be evaluated.
(t (setf my-string (concatenate 'string lisp-code-string my-char)))))
(t (error "invalid current mode"))))))
;;; #a is the input which starts the custom reader.
(set-dispatch-macro-character #\# #\a #'transform-code-to-string))
这里有一些示例汇编代码，里面没有Lisp代码，有效：
(defparameter *example-code-x64* #a inc r10 ; increment register r10. mov r11,r12 ; store value of r12 into r11. #e)
这里有一些内置Lisp代码的汇编代码，失败（请参阅下面的编译错误）。在这一个中，Lisp代码在汇编代码之后，但是应该允许使用#a和#l作为分隔符自由混合汇编和Lisp代码。
(defparameter *example-code-x64-with-lisp-fails*
#a
inc r10 ; increment register r10.
mov r11,r12 ; store value of r12 into r11.
#l
(loop for current-instruction in (list "inc" "dec")
do (loop for current-arg in (list "r13" "r14" "r15")
do (princ (concatenate 'string
current-instruction
" "
current-arg
(coerce (list #\Newline) 'string)))))
#e)
上述代码的Lisp部分应该在自定义阅读器中进行评估，以便它应该产生与下面代码相同的结果：
(defparameter *example-code-x64-with-lisp-fails* #a inc r10 ; increment register r10. mov r11,r12 ; store value of r12 into r11. inc r13 inc r14 inc r15 dec r13 dec r14 dec r15 #e)
但是编译失败了：
CL-USER> ; compiling file "/home/user/code/lisp/lisp-asm-reader-for-stackoverflow.lisp" (written 28 MAR 2014 10:11:29 PM): ; ; caught ERROR: ; READ error during COMPILE-FILE: ; ; The value -1 is not of type (MOD 4611686018427387901). ; ; (in form starting at line: 1, column: 0, file-position: 0) ; ; compilation unit aborted ; caught 1 fatal ERROR condition ; caught 1 ERROR condition ; compilation aborted after 0:00:00.004 1 compiler notes: /home/user/code/lisp/lisp-asm-reader-for-stackoverflow.lisp:10487 read-error: READ error during COMPILE-FILE: The value -1 is not of type (MOD 4611686018427387901). (in form starting at line: 1, column: 0, file-position: 0) CL-USER>
答案 0 :(得分：5)
从读取器宏中读取lisp代码的惯用方法是调用cl：read。在您的示例中，在使用#L之后调用read将返回其car为循环的列表，并且该列表可以传递给eval。
要收集在eval期间创建的输出，您可以绑定* standard-output *。因此，选择是在阅读器宏中使用类似于以下内容的内容：
(let ((lisp-printed-string
(with-output-to-string (*standard-output*)
(eval (read stream t t t)))))
;; concatenate the lisp printed string onto your
;; hand parsed string here
)
另一种方法是让用户输入一个返回字符串的lisp表单{例如（连接＆＃34; bar＆＃34;＆＃34; baz＆＃34;）}，并收集eval的返回值而不是其打印输出。