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Update chapter-11.lisp #9

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12 changes: 5 additions & 7 deletions src/chapter-11.lisp
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Original file line number Diff line number Diff line change
Expand Up @@ -151,22 +151,20 @@

;; p. 156

;; problem reported to pg but not checked -- test this!!!!!!!!!!
;; The problem reported to pg listed at
;; http://www.paulgraham.com/onlisperrata.html:
;; p. 156. In do-tuples/o the expression (1- (length parms)) should be
;; "p. 156. In do-tuples/o the expression (1- (length parms)) should be
;; (- (length source) (length parms)).
;; Reported by Roland. (at netquant.com.br)
;; Reported by Roland. (at netquant.com.br)"
;; is wrong, the original text below has the correct code.
(defmacro do-tuples/o (parms source &body body)
(if parms
(let ((src (gensym)))
`(prog ((,src ,source))
(mapc (lambda ,parms ,@body)
,@(map0-n (lambda (n)
`(nthcdr ,n ,src))
;;(1- (length parms)) ;; error in text
(- (length source) (length parms)) ;; corrected

))))))
(1- (length parms))))))))

(defmacro do-tuples/c (parms source &body body)
(if parms
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