Remember that remove returns a copy of the list. It doesn't change the original list. So (apply #'+ lst) is still referring to the original list. Try (defun summit (lst) (apply #'+ (remove nil lst))) Happy learning. It's an enlightening journey. Laughing Water On Jan 19, 2008, at 12:35 PM, He Jibo wrote: > Hi, Everyone, > > I am starting to learn Lisp. Could you please bother to help me on > the following question? Thank you! > > I plan to write a function that returns the sum of all non-nil > numbers in a list. However, it does not work as intended. Could you > please tell me what is the problem and how to correct it? Thank you > so much . > The function I wrote is as follows: > (defun (summit ( lst) (remove nil lst) (apply #' + lst)) > > Thanks! :-) > >
Firstly, the syntax of defun is (defun <name> <args> <body>) So you want (defun summit (lst) ...) Secondly, remove is a function. It doesn't alter its arguments, it returns a new list. Consider typing these forms in the listener: > (setf list '(1 2 3)) ==> (1 2 3) > (remove 2 list) ==> (1 3) > list ==> (1 2 3) The call to remove returned what I want but my list is the same after the call. Lastly, you may want to look up the function reduce. Regards. On Jan 19, 2008, at 2:35 PM, He Jibo wrote: > Hi, Everyone, > > I am starting to learn Lisp. Could you please bother to help me on > the following question? Thank you! > > I plan to write a function that returns the sum of all non-nil > numbers in a list. However, it does not work as intended. Could you > please tell me what is the problem and how to correct it? Thank you > so much . > The function I wrote is as follows: > (defun (summit ( lst) (remove nil lst) (apply #' + lst)) > > Thanks! :-) > > -- Gary Warren King, metabang.com Cell: (413) 559 8738 Fax: (206) 338-4052 gwkkwg on Skype * garethsan on AIM
He Jibo wrote: > I plan to write a function that returns the sum of all non-nil numbers > in a list. However, it does not work as intended. Could you please tell > me what is the problem and how to correct it? Thank you so much . > The function I wrote is as follows: > (defun (summit ( lst) (remove nil lst) (apply #' + lst)) 1. No parenthesis between defun and summit. 2. (remove nil lst) doesn't change lst, it returns a list which you can subsequently use. So: (defun summit (lst) (apply #'+ (remove nil lst))) reduce could be used instead of apply, but I don't know if that is an improvement. It is likely that someone will mention that this list is primarily, if not exclusively for Lispworks-specific topics. But I enjoy the infrequent occasion when I can offer an answer. Mitch
On 19-Jan-08, at 12:35 PM, He Jibo wrote: > Hi, Everyone, > > I am starting to learn Lisp. Could you please bother to help me on > the following question? Thank you! > > I plan to write a function that returns the sum of all non-nil > numbers in a list. However, it does not work as intended. Could you > please tell me what is the problem and how to correct it? Thank you > so much . > The function I wrote is as follows: > (defun (summit ( lst) (remove nil lst) (apply #' + lst)) > > Thanks! :-) > > For something like that I would not use remove. Just iterate through the list and sum the non nils. (defun sum-non-nil (list) (loop for n in list when n sum n)) Wade
By the way, from one newbie to another, I do suggest that you learn to use loop (see ). Lots of details yes, but definitely grounds for an aha. It is powerful.
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