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Old 07-09-2010, 02:03 PM   #1
zaxonus
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Registered: Jul 2005
Posts: 53

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Common Lisp functions.


Hello,

I have written 2 functions, this way :

(let ((sum 10))
(defun ACC10 (x) (setf sum (+ sum x))))

(let ((sum 50))
(defun ACC50 (x) (setf sum (+ sum x))))

I don't know if I am following good Lisp practices here; but the 2 functions do what I want.
Each of them keeps track of an internal value and I can make calls like :

(ACC10 5)
(ACC10 4)
(ACC10 -3)
(ACC50 -15)
(ACC50 22)
(ACC10 7)
(ACC50 13)
... etc ... each function is doing its book-keeping job.

My first question is :

To write say ACC97; could I start like ?

(defun ACC97 (x)
(let ((sum 97)) ....

instead of like before :
(let ((sum 97))
(defun ACC97 (x) ....

If yes what is the proper syntax ? Since what I tried did not work.

My second question is :
Would it be possible to write a function make-ACC that I could use to genarate my ACC functions above ?
For example in order to make ACC97 I would use something like :
(make-ACC 97)
and in the same way to make ACC50 I would use :
(make-ACC 50)

Here also what I tried did not quite work.

Thanks for any tip.
 
Old 07-09-2010, 02:13 PM   #2
Sergei Steshenko
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Registered: May 2005
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Quote:
Originally Posted by zaxonus View Post
... Would it be possible to write a function make-ACC that I could use to genarate my ACC functions above ? ...
I am not a LISP guy, but isn't it what macros in LISP are for ?
 
Old 07-09-2010, 05:30 PM   #3
ntubski
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Registered: Nov 2005
Distribution: Debian, Arch
Posts: 3,387

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This is just Paul Graham's Accumulator Generator:
Code:
(defun foo (n) (lambda (i) (incf n i)))
 
  


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