LispForum

Posted: **Mon Jul 25, 2011 3:36 pm**

(defun add ()
...(let ((sum 0) next)
......(loop
.........(setq next (read))
.........(cond ((numberp next) (incf sum next))
............(eq '= next) (print sum) (return))
............(t (format t "~&~a ignored~%" next))))
.......(values)))

I thought the structure of a let is:

(let (bindings) forms)
where (bindings) is any number of two-element lists:

Code: Select all

(let ((a 0)
       (b 1))
  (form))

Above, (let ((sum 0) next) ...
does not seem to follow that rule

(BTW: How do I write lisp code here so that it is nicelfy formatted --- sorry - haven't had a chance to read the FAQ yet -- I will)

Posted: **Mon Jul 25, 2011 6:14 pm**

When no value is given to a variable being declared with let, it is assigned to NIL

Therefore, this:

Code: Select all

(let ((sum 0) next)
  ...)

this:

Code: Select all

(let ((sum 0) (next))
  ...)

and this:

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(let ((sum 0) (next nil))
  ...)

they all mean the same thing.

Note: to insert Lisp code in this forum, put it like this:

Code: Select all

[code]<Lisp code here>

[/code]

Posted: **Tue Jul 26, 2011 9:05 am**

Thanks. That allows me to move forward. As you said, all of these are equivalent:

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(let ((a 0) b)
 
(let ((a 0)
      (b nil))

(let ((a 0)
      (b))

I like the middle one because it "follows the rules".

Posted: **Tue Jul 26, 2011 10:35 am**

You are welcome

Posted: **Tue Jul 26, 2011 2:54 pm**

amachina wrote:Thanks. That allows me to move forward. As you said, all of these are equivalent:
Code: Select all
(let ((a 0) b)
 
(let ((a 0)
      (b nil))

(let ((a 0)
      (b))
I like the middle one because it "follows the rules".

They all "follow the rules"...

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