附录 B：Lisp in Lisp

这个附录包含了 58 个最常用的 Common Lisp 操作符。因为如此多的 Lisp 是（或可以）用 Lisp 所写成，而由于 Lisp 程序（或可以）相当精简，这是一种方便解释语言的方式。

这个练习也证明了，概念上 Common Lisp 不像看起来那样庞大。许多 Common Lisp 操作符是有用的函式库；要写出所有其它的东西，你所需要的操作符相当少。在这个附录的这些定义只需要:

apply aref backquote block car cdr ceiling char= cons defmacro documentation eq error expt fdefinition function floor gensym get-setf-expansion if imagpart labels length multiple-value-bind nth-value quote realpart symbol-function tagbody type-of typep = + - / < >

这里给出的代码作为一种解释 Common Lisp 的方式，而不是实现它的方式。在实际的实现上，这些操作符可以更高效，也会做更多的错误检查。为了方便参找，这些操作符本身按字母顺序排列。如果你真的想要这样定义 Lisp，每个宏的定义需要在任何调用它们的代码之前。

(defun -abs (n)
  (if (typep n 'complex)
      (sqrt (+ (expt (realpart n) 2) (expt (imagpart n) 2)))
      (if (< n 0) (- n) n)))

(defun -adjoin (obj lst &rest args)
  (if (apply #'member obj lst args) lst (cons obj lst)))

(defmacro -and (&rest args)
  (cond ((null args) t)
        ((cdr args)  `(if ,(car args) (-and ,@(cdr args))))
        (t           (car args))))

(defun -append (&optional first &rest rest)
  (if (null rest)
      first
      (nconc (copy-list first) (apply #'-append rest))))

(defun -atom (x) (not (consp x)))

(defun -butlast (lst &optional (n 1))
  (nreverse (nthcdr n (reverse lst))))

(defun -cadr (x) (car (cdr x)))

(defmacro -case (arg &rest clauses)
  (let ((g (gensym)))
    `(let ((,g ,arg))
       (cond ,@(mapcar #'(lambda (cl)
                           (let ((k (car cl)))
                             `(,(cond ((member k '(t otherwise))
                                       t)
                                      ((consp k)
                                       `(member ,g ',k))
                                      (t `(eql ,g ',k)))
                               (progn ,@(cdr cl)))))
                       clauses)))))

(defun -cddr (x) (cdr (cdr x)))

(defun -complement (fn)
  #'(lambda (&rest args) (not (apply fn args))))

(defmacro -cond (&rest args)
  (if (null args)
      nil
      (let ((clause (car args)))
        (if (cdr clause)
            `(if ,(car clause)
                 (progn ,@(cdr clause))
                 (-cond ,@(cdr args)))
            `(or ,(car clause)
                 (-cond ,@(cdr args)))))))

(defun -consp (x) (typep x 'cons))

(defun -constantly (x) #'(lambda (&rest args) x))

(defun -copy-list (lst)
  (labels ((cl (x)
             (if (atom x)
                 x
                 (cons (car x)
                       (cl (cdr x))))))
    (cons (car lst)
          (cl (cdr lst)))))

(defun -copy-tree (tr)
  (if (atom tr)
      tr
      (cons (-copy-tree (car tr))
            (-copy-tree (cdr tr)))))

(defmacro -defun (name parms &rest body)
  (multiple-value-bind (dec doc bod) (analyze-body body)
    `(progn
       (setf (fdefinition ',name)
             #'(lambda ,parms
                 ,@dec
                 (block ,(if (atom name) name (second name))
                   ,@bod))
             (documentation ',name 'function)
             ,doc)
       ',name)))

(defun analyze-body (body &optional dec doc)
  (let ((expr (car body)))
    (cond ((and (consp expr) (eq (car expr) 'declare))
           (analyze-body (cdr body) (cons expr dec) doc))
          ((and (stringp expr) (not doc) (cdr body))
           (if dec
               (values dec expr (cdr body))
               (analyze-body (cdr body) dec expr)))
          (t (values dec doc body)))))

这个定义不完全正确，参见 let

(defmacro -do (binds (test &rest result) &rest body)
  (let ((fn (gensym)))
    `(block nil
       (labels ((,fn ,(mapcar #'car binds)
                   (cond (,test ,@result)
                         (t (tagbody ,@body)
                            (,fn ,@(mapcar #'third binds))))))
         (,fn ,@(mapcar #'second binds))))))

(defmacro -dolist ((var lst &optional result) &rest body)
  (let ((g (gensym)))
    `(do ((,g ,lst (cdr ,g)))
         ((atom ,g) (let ((,var nil)) ,result))
       (let ((,var (car ,g)))
         ,@body))))

(defun -eql (x y)
  (typecase x
    (character (and (typep y 'character) (char= x y)))
    (number    (and (eq (type-of x) (type-of y))
                    (= x y)))
    (t         (eq x y))))

(defun -evenp (x)
  (typecase x
    (integer (= 0 (mod x 2)))
    (t       (error "non-integer argument"))))

(defun -funcall (fn &rest args) (apply fn args))

(defun -identity (x) x)

这个定义不完全正确：表达式 (let ((&key 1) (&optional 2))) 是合法的，但它产生的表达式不合法。

(defmacro -let (parms &rest body)
  `((lambda ,(mapcar #'(lambda (x)
                         (if (atom x) x (car x)))
                     parms)
      ,@body)
    ,@(mapcar #'(lambda (x)
                  (if (atom x) nil (cadr x)))
              parms)))

(defun -list (&rest elts) (copy-list elts))

(defun -listp (x) (or (consp x) (null x)))

(defun -mapcan (fn &rest lsts)
  (apply #'nconc (apply #'mapcar fn lsts)))

(defun -mapcar (fn &rest lsts)
  (cond ((member nil lsts) nil)
        ((null (cdr lsts))
         (let ((lst (car lsts)))
           (cons (funcall fn (car lst))
                 (-mapcar fn (cdr lst)))))
        (t
         (cons (apply fn (-mapcar #'car lsts))
               (apply #'-mapcar fn
                      (-mapcar #'cdr lsts))))))

(defun -member (x lst &key test test-not key)
  (let ((fn (or test
                (if test-not
                    (complement test-not))
                    #'eql)))
    (member-if #'(lambda (y)
                   (funcall fn x y))
               lst
               :key key)))

(defun -member-if (fn lst &key (key #'identity))
  (cond ((atom lst) nil)
        ((funcall fn (funcall key (car lst))) lst)
        (t (-member-if fn (cdr lst) :key key))))

(defun -mod (n m)
  (nth-value 1 (floor n m)))

(defun -nconc (&optional lst &rest rest)
  (if rest
      (let ((rest-conc (apply #'-nconc rest)))
        (if (consp lst)
            (progn (setf (cdr (last lst)) rest-conc)
                   lst)
            rest-conc))
      lst))

(defun -not (x) (eq x nil))
(defun -nreverse (seq)
  (labels ((nrl (lst)
             (let ((prev nil))
               (do ()
                   ((null lst) prev)
                 (psetf (cdr lst) prev
                        prev      lst
                        lst       (cdr lst)))))
           (nrv (vec)
             (let* ((len (length vec))
                    (ilimit (truncate (/ len 2))))
               (do ((i 0 (1+ i))
                    (j (1- len) (1- j)))
                   ((>= i ilimit) vec)
                 (rotatef (aref vec i) (aref vec j))))))
    (if (typep seq 'vector)
        (nrv seq)
        (nrl seq))))

(defun -null (x) (eq x nil))

(defmacro -or (&optional first &rest rest)
  (if (null rest)
      first
      (let ((g (gensym)))
        `(let ((,g ,first))
           (if ,g
               ,g
               (-or ,@rest))))))

这两个 Common Lisp 没有，但这里有几的定义会需要用到。

(defun pair (lst)
  (if (null lst)
      nil
      (cons (cons (car lst) (cadr lst))
            (pair (cddr lst)))))
(defun -pairlis (keys vals &optional alist)
  (unless (= (length keys) (length vals))
    (error "mismatched lengths"))
  (nconc (mapcar #'cons keys vals) alist))

(defmacro -pop (place)
  (multiple-value-bind (vars forms var set access)
                       (get-setf-expansion place)
    (let ((g (gensym)))
      `(let* (,@(mapcar #'list vars forms)
              (,g ,access)
              (,(car var) (cdr ,g)))
         (prog1 (car ,g)
                ,set)))))

(defmacro -prog1 (arg1 &rest args)
  (let ((g (gensym)))
    `(let ((,g ,arg1))
       ,@args
       ,g)))

(defmacro -prog2 (arg1 arg2 &rest args)
  (let ((g (gensym)))
    `(let ((,g (progn ,arg1 ,arg2)))
       ,@args
       ,g)))

(defmacro -progn (&rest args) `(let nil ,@args))

(defmacro -psetf (&rest args)
  (unless (evenp (length args))
    (error "odd number of arguments"))
  (let* ((pairs (pair args))
         (syms (mapcar #'(lambda (x) (gensym))
                       pairs)))
    `(let ,(mapcar #'list
                   syms
                   (mapcar #'cdr pairs))
       (setf ,@(mapcan #'list
                       (mapcar #'car pairs)
                       syms)))))

(defmacro -push (obj place)
  (multiple-value-bind (vars forms var set access)
                       (get-setf-expansion place)
    (let ((g (gensym)))
      `(let* ((,g ,obj)
              ,@(mapcar #'list vars forms)
              (,(car var) (cons ,g ,access)))
         ,set))))

(defun -rem (n m)
  (nth-value 1 (truncate n m)))
(defmacro -rotatef (&rest args)
  `(psetf ,@(mapcan #'list
                    args
                    (append (cdr args)
                            (list (car args))))))

(defun -second (x) (cadr x))
(defmacro -setf (&rest args)
  (if (null args)
      nil
      `(setf2 ,@args)))

(defmacro setf2 (place val &rest args)
  (multiple-value-bind (vars forms var set)
                       (get-setf-expansion place)
    `(progn
       (let* (,@(mapcar #'list vars forms)
              (,(car var) ,val))
         ,set)
       ,@(if args `((setf2 ,@args)) nil))))

(defun -signum (n)
  (if (zerop n) 0 (/ n (abs n))))

(defun -stringp (x) (typep x 'string))

(defun -tailp (x y)
  (or (eql x y)
      (and (consp y) (-tailp x (cdr y)))))

(defun -third (x) (car (cdr (cdr x))))

(defun -truncate (n &optional (d 1))
  (if (> n 0) (floor n d) (ceiling n d)))

(defmacro -typecase (arg &rest clauses)
  (let ((g (gensym)))
    `(let ((,g ,arg))
       (cond ,@(mapcar #'(lambda (cl)
                           `((typep ,g ',(car cl))
                             (progn ,@(cdr cl))))
                       clauses)))))

(defmacro -unless (arg &rest body)
  `(if (not ,arg)
       (progn ,@body)))

(defmacro -when (arg &rest body)
  `(if ,arg (progn ,@body)))

(defun -1+ (x) (+ x 1))

(defun -1- (x) (- x 1))

(defun ->= (first &rest rest)
  (or (null rest)
      (and (or (> first (car rest)) (= first (car rest)))
           (apply #'->= rest))))