DO，PROG等在他们的身体周围建立一个名为nil的隐式块。 CLHS不提供执行此操作的所有标准宏的列表。到目前为止，我所知道的是：
DO
DO*
PROG
PROG*
LOOP
DOLIST
DOTIMES
DO-SYMBOLS
DO-ALL-SYMBOLS
DO-EXTERNAL-SYMBOLS
是否有其他标准CL宏或特殊形式建立隐式nil块？
答案 0 :(得分：9)
我相信问题清单已经完成。我的证据是实验性的，而不是检查CLHS的每一页;这就是我所做的，为了任何想要检查的人的利益，我没有错过任何重要的事情。最后有一个警告清单。
首先，一个简单的函数来检查宏扩展是否有一个名为NIL的块。它会找到不在顶层的NIL块。它可能有误报，因此输出需要手动检查。
(defun has-nil-block (x)
(labels ((helper (items)
(and (consp items) (or (has-nil-block (first items)) (helper (rest items))))))
(and (consp x) (or (and (eq (first x) 'block) (eq (second x) nil))
(helper x)))))
然后我选择了最方便的CL实现，恰好是CLISP，并且这样做了：
(let ((syms nil))
(do-symbols (sym (find-package "COMMON-LISP"))
(when (macro-function sym) (push sym syms)))
syms)
给了我以下列表（没有特别的顺序，包括重复的符号，包括一些但不是所有在CLHS中定义为特殊运算符的符号）：
(CALL-METHOD GENERIC-FLET WITH-SLOTS GENERIC-LABELS CLOS-WARNING DEFGENERIC
DEFINE-METHOD-COMBINATION MAKE-METHOD DEFMETHOD DEFCLASS WITH-ACCESSORS
DO-EXTERNAL-SYMBOLS DOTIMES ROTATEF ETYPECASE IGNORE-ERRORS CHECK-TYPE
TYPECASE MAKE-METHOD DEFMETHOD CTYPECASE WITH-SLOTS WITH-PACKAGE-ITERATOR
HANDLER-BIND LAMBDA ECASE DEFINE-MODIFY-MACRO DECF DEFCLASS DEFPARAMETER
DESTRUCTURING-BIND WITH-SIMPLE-RESTART POP WITH-OUTPUT-TO-STRING
DEFINE-CONDITION DEFUN STEP WITH-OPEN-FILE AND MULTIPLE-VALUE-SETQ COND
CALL-METHOD DEFCONSTANT DEFMACRO WHEN MULTIPLE-VALUE-LIST UNTRACE PROG2
DEFGENERIC PROG1 PUSHNEW PROG* DEFTYPE DEFINE-METHOD-COMBINATION
WITH-OPEN-STREAM OR WITH-ACCESSORS SHIFTF INCF PUSH HANDLER-CASE NTH-VALUE
DEFSTRUCT RESTART-CASE PSETQ WITH-INPUT-FROM-STRING ASSERT SETF PSETF
DEFPACKAGE LOOP-FINISH WITH-STANDARD-IO-SYNTAX DEFINE-SYMBOL-MACRO TIME
IN-PACKAGE FORMATTER DO-SYMBOLS CASE LOCALLY DO REMF DO* WITH-COMPILATION-UNIT
LOOP RETURN WITH-CONDITION-RESTARTS PPRINT-LOGICAL-BLOCK CCASE TRACE DEFVAR
PRINT-UNREADABLE-OBJECT DEFINE-COMPILER-MACRO PROG RESTART-BIND DO-ALL-SYMBOLS
UNLESS DECLAIM DEFINE-SETF-EXPANDER MULTIPLE-VALUE-BIND DEFSETF
WITH-HASH-TABLE-ITERATOR DOLIST DECLARE)
然后我将这些与CLHS第3.1.2.1.2.1节中列出的特殊操作符一起删除了CLHS中未提及的那些，删除了重复项，为每个操作符编写了一个典型的调用（在某些操作中不止一个） case），然后检查每个上面调用MACROEXPAND-1和MACROEXPAND的结果：
(let ((candidates '(
;; special operators as defined in CLHS 3.1.2.1.2.1
(block wombat)
(catch a-tag t)
(eval-when (:compile-toplevel :load-toplevel :execute) t)
(flet ((f (x) x)) (f t))
(function (x) t)
(go bananas)
(if (some-function) 123 234)
(labels ((f (x) x) (g (x) (1+ (f x)))) (g (banana)))
(let ((x 1) (y 2)) (+ x y))
(let* ((x 1) (y 2)) (+ x y))
(load-time-value 123)
(load-time-value 123 t)
(locally (declare (special x)) x)
(macrolet ((zog (x) x)) (zog 123))
(multiple-value-call #'list 1 (values 2 3) 4)
(multiple-value-prog1 (values 1 2) (values 2 3))
(progn (f) (g) (h))
(progv '(*x* *y* *z*) '(1 2 3) (+ *x* *y* *z*))
(quote 123)
(return-from some-name 123)
(setq x 1 y 2 z 3)
(symbol-macrolet ((x '(foo x))) (list x))
(tagbody (foo) x (bar) (go x))
(the double-float 1.234d0)
(throw 'ouch 123)
(unwind-protect (foo) (bar))
;; symbols in COMMON-LISP package for which MACRO-FUNCTION evaluates to true in CLISP
;(call-method (make-method t)) ;; this is kinda illegal
(with-slots ((xx x) (yy y)) an-object (list xx yy))
(defgeneric f (a b) (:method ((a integer) (b integer)) 123))
(define-method-combination fnord :identity-with-one-argument t)
(define-method-combination zorg () ((around (:around)) (primary (zorg) :required t)) t)
(defmethod foo ((a double-float) b) (+ a b))
(with-accessors ((xx x) (yy y)) an-object (list xx yy))
(do-symbols (sym :COMMON-LISP) nil)
(do-all-symbols (sym :COMMON-LISP) nil)
(do-external-symbols (sym :COMMON-LISP) nil)
(do (x (y 1 2)) ((ended) (final x y)) (foo x y))
(do* (x (y 1 2)) ((ended) (final x y)) (foo x y))
(dotimes (i 3) (foo i))
(dolist (x (get-list)) (foo x))
(rotatef a b c)
(shiftf a b c)
(typecase an-object ((integer 1) (otherwise 2)))
(ctypecase an-object ((integer 1) (otherwise 2)))
(etypecase an-object ((integer 1) (otherwise 2)))
(ignore-errors (foo))
(check-type x integer)
(handler-bind ((unbound-variable #'(lambda (x) x))) (foo))
(handler-case (foo) (unbound-variable (c) (bar c)))
(lambda (x) x)
(case x ((1) t) (otherwise 'zog))
(ccase x ((1) t) (otherwise 'zog))
(ecase x ((1) t) (otherwise 'zog))
(decf x)
(incf x)
(defconstant +x+ 123)
(defparameter *x* 123)
(defvar *x* 123)
(deftype zoo () `(and (array) (satisfies (lambda (a) (eql (array-rank a) 1)))))
(defstruct boo slot1 slot2)
(defstruct (boo :constructor :copier :predicate (:print-object pfun)) slot1 slot2)
(defclass trivclass () ())
(defpackage :SOME-PACKAGE)
(in-package :SOME-PACKAGE (foo))
(with-package-iterator (iter :COMMON-LISP :internal :external :inherited) 123)
(with-package-iterator (iter :COMMON-LISP :internal :external :inherited) (foo (iter)))
(with-hash-table-iterator (iter (get-hash-table)) (foo (iter)))
(destructuring-bind (x y) (foo) (list y x))
(with-simple-restart (abort "Exit") (foo))
(restart-bind ((my-restart (get-restart-function))) (foo))
(restart-case (foo) (my-restart (x) x))
(with-condition-restarts (get-condition) (get-restarts) (foo))
(push (foo) some-list)
(pushnew (foo) some-list)
(pop some-list)
(with-input-from-string (ss (get-string)) (foo ss))
(with-output-to-string (ss) (foo ss))
(define-condition my-condition () ())
(defun foo () 123)
(defmacro foo (&rest body) body)
(define-symbol-macro foo (call-foo))
(define-modify-macro appendf (&rest args) append "Append onto list")
(define-compiler-macro foo (&rest body) `(call-foo . ,body))
(defsetf accessor updater)
(defsetf accessor (x spong) (result) result)
(step (foo))
(with-open-file (ss (get-filespec) :direction :input) (foo ss))
(with-open-stream (st (get-stream)) (foo st))
(and (foo) (bar) (baz))
(or (foo) (bar) (baz))
(multiple-value-setq (x y z) (foo))
(multiple-value-list (foo))
(psetq x 1 y 2 z 3)
(psetf x 1 y 2 z 3)
(setf x 1 y 2 z 3)
(remf (car x) 'property)
(cond ((foo) 123) ((bar) 321) (t 999))
(when (foo) (bar) (baz))
(unless (foo) (bar) (baz))
(trace banana)
(untrace banana)
(prog1 (foo) (bar) (baz))
(prog2 (foo) (bar) (baz))
(prog (x y z) (foo x) aaa (foo y) (go aaa) (foo z))
(prog* (x y z) (foo x) aaa (foo y) (go aaa) (foo z))
(nth-value (get-index) (get-values))
(assert (foo))
(with-standard-io-syntax (foo))
(time (foo))
(formatter "~&~A~%")
(with-compilation-unit () (foo))
(loop (foo))
(loop for x in (foo) do (bar x))
(return 123)
(pprint-logical-block (stream thing) (foo))
(print-unreadable-object (obj stream) (foo))
(declare ((optimize (space 0))))
)))
(loop for candidate in candidates do
(let ((one (macroexpand-1 candidate))
(two (macroexpand candidate)))
(cond ((has-nil-block one)
(format t "~&~%~A~% ==> ~A~%" candidate one))
((has-nil-block two)
(format t "~&~%~A~% ==> ~A~% ...--> ~A~%" candidate one two))))))
对于任何候选宏调用，报告（1）是否直接扩展（通过MACROEXPAND-1）到其中有（BLOCK NIL ...）的东西，以及（2）如果没有，是否将indirectlY（通过MACROEXPAND）扩展为带有（BLOCK NIL ...）的东西。它显示了宏扩展，以便您可以确保它们不是误报。
这是结果（我已经发现了一些警告信息）：
(DO-SYMBOLS (SYM COMMON-LISP) NIL)
==>
(BLOCK NIL
(LET ((PACKAGE-4169 COMMON-LISP))
(LET ((SYM NIL)) (DECLARE (IGNORABLE SYM))
(MAP-SYMBOLS #'(LAMBDA (SYM) (TAGBODY NIL)) PACKAGE-4169) NIL)))
(DO-ALL-SYMBOLS (SYM COMMON-LISP) NIL)
==>
(BLOCK NIL
(LET ((SYM NIL)) (DECLARE (IGNORABLE SYM)) (MAP-ALL-SYMBOLS #'(LAMBDA (SYM) (TAGBODY NIL)))
COMMON-LISP))
(DO-EXTERNAL-SYMBOLS (SYM COMMON-LISP) NIL)
==>
(BLOCK NIL
(LET ((PACKAGE-4171 COMMON-LISP))
(LET ((SYM NIL)) (DECLARE (IGNORABLE SYM))
(MAP-EXTERNAL-SYMBOLS #'(LAMBDA (SYM) (TAGBODY NIL)) PACKAGE-4171) NIL)))
(DO (X (Y 1 2)) ((ENDED) (FINAL X Y)) (FOO X Y))
==>
(BLOCK NIL
(LET (X (Y 1))
(TAGBODY LOOP-4173 (IF (ENDED) (GO END-4174)) (FOO X Y) (PSETQ Y 2) (GO LOOP-4173) END-4174
(RETURN-FROM NIL (PROGN (FINAL X Y))))))
(DO* (X (Y 1 2)) ((ENDED) (FINAL X Y)) (FOO X Y))
==>
(BLOCK NIL
(LET* (X (Y 1))
(TAGBODY LOOP-4177 (IF (ENDED) (GO END-4178)) (FOO X Y) (SETQ Y 2) (GO LOOP-4177) END-4178
(RETURN-FROM NIL (PROGN (FINAL X Y))))))
(DOTIMES (I 3) (FOO I))
==> (DO ((I 0 (1+ I))) ((>= I 3) NIL) (FOO I))
...-->
(BLOCK NIL
(LET ((I 0))
(TAGBODY LOOP-4181 (IF (>= I 3) (GO END-4182)) (FOO I) (PSETQ I (1+ I)) (GO LOOP-4181) END-418
(RETURN-FROM NIL (PROGN NIL)))))
(DOLIST (X (GET-LIST)) (FOO X))
==>
(DO* ((LIST-4183 (GET-LIST) (CDR LIST-4183)) (X NIL)) ((ENDP LIST-4183) NIL)
(DECLARE (LIST LIST-4183)) (SETQ X (CAR LIST-4183)) (FOO X))
...-->
(BLOCK NIL
(LET* ((LIST-4184 (GET-LIST)) (X NIL)) (DECLARE (LIST LIST-4184))
(TAGBODY LOOP-4185 (IF (ENDP LIST-4184) (GO END-4186)) (SETQ X (CAR LIST-4184)) (FOO X)
(SETQ LIST-4184 (CDR LIST-4184)) (GO LOOP-4185) END-4186 (RETURN-FROM NIL (PROGN NIL)))))
(PROG (X Y Z) (FOO X) AAA (FOO Y) (GO AAA) (FOO Z))
==> (BLOCK NIL (LET (X Y Z) (TAGBODY (FOO X) AAA (FOO Y) (GO AAA) (FOO Z))))
(PROG* (X Y Z) (FOO X) AAA (FOO Y) (GO AAA) (FOO Z))
==> (BLOCK NIL (LET* (X Y Z) (TAGBODY (FOO X) AAA (FOO Y) (GO AAA) (FOO Z))))
(LOOP (FOO))
==> (BLOCK NIL (TAGBODY LOOP-4350 (FOO) (GO LOOP-4350)))
(LOOP FOR X IN (FOO) DO (BAR X))
==>
(MACROLET ((LOOP-FINISH NIL (LOOP-FINISH-ERROR)))
(BLOCK NIL
(LET ((LIST-4352 (FOO)))
(PROGN
(LET ((X NIL))
(LET NIL
(MACROLET ((LOOP-FINISH NIL '(GO END-LOOP)))
(TAGBODY BEGIN-LOOP (WHEN (ENDP LIST-4352) (LOOP-FINISH)) (SETQ X (CAR LIST-4352))
(PROGN (PROGN (BAR X))) (PSETQ LIST-4352 (CDR LIST-4352)) (GO BEGIN-LOOP) END-LOOP
(MACROLET ((LOOP-FINISH NIL (LOOP-FINISH-WARN) '(GO END-LOOP))))))))))))
包括原始问题中列出的所有符号而不包含其他符号。
这可能出错的方法：（1）调用给定的宏是否产生nil块可能取决于调用的细节。我故意为所有的宏选择了很好的简单调用，并且（例如）一些更为巴洛克式的DEFCLASS实例可能会创建一个创建nil块的东西。 （2）我可能错过了宏列表中的一些项目。 （我的候选列表在CLISP输出的顺序中有点排序，但我重新排列了一下以将相关的宏放在一起。）（3）CLISP在相关方面可能是非标准的。
我相当确信这些都不会导致我的结果无效。将“相当自信”变为“接近绝对肯定”可能意味着将所需工作量增加一倍： - ）。