<div>I finished it. The purpose of the function is to count the occurrance of a letter in a list. Ex:</div> <div> </div> <div>(count-matches 'x '()) should be 0</div> <div>(count-matches 'x '(a b x)) should be 1 </div> <div>(count-matches 'x '(x b x)) should be 2 </div> <div> </div> <div>The keywords I can use are limited. Thank you all for the help. Another I need to write is to remove duplicated items from the list.</div> <div> </div> <div>It seems that under cond, one condition can only take one expression. What can I do if I want to do two statements?</div> <div> </div> <div>Here is the code. </div> <div> </div> <div>(define (count-matches s l) <br> (define (addone s l x)<br> (cond<br> [(empty? l) x]<br> [(equal? s (first l)) (addone s (rest l) (+ 1 x))]<br> [else (addone s (rest l) x)]))<br> (addone s l 0))</div> <div> </div> <div> </div> <div class="gmail_quote">On Tue, May 31, 2011 at 12:31 PM, Yingjian Ma <span dir="ltr"><<a href="mailto:yingjian.ma1955@gmail.com">yingjian.ma1955@gmail.com</a>></span> wrote:<br> <blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote">Thank you for letting me know. I'll use the user list instead of this board in the future. <div> <div></div> <div class="h5"><br> <div class="gmail_quote"> </div> <div class="gmail_quote">On Tue, May 31, 2011 at 10:59 AM, Stephen Bloch <span dir="ltr"><<a href="mailto:sbloch@adelphi.edu" target="_blank">sbloch@adelphi.edu</a>></span> wrote:<br> <blockquote style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex" class="gmail_quote"> <div><br>On May 31, 2011, at 12:01 PM, Yingjian Ma wrote:<br><br></div> <div>> I am new to Racket. I did not expect that output is "#<procedure:...uments...". It is like an error message to me.<br><br></div>Of course you didn't expect it; that's the way bugs happen. Marijn's point is that the "#<procedure: ..." is actually the RETURNED VALUE from your function, not an error message. The real question is, why is your function returning a function rather than a number? (It's the "lambda".)<br> <br>Have you written a collection of test cases for this function? Have you listed, inside the body of the function, an "inventory" of available expressions you're likely to need? You're correctly testing whether the list is empty, and if not, you're correctly testing whether the first thing in the list matches what you're looking for, but if it is, you're returning a function rather than a number as I think you intended.<br> <br>And as somebody pointed out, this sort of question belongs on the racket or plt-edu list, not on the racket-dev list (which is for people developing and maintaining Racket itself, not people learning to program in it).<br> <font color="#888888"><br><br>Stephen Bloch<br><a href="mailto:sbloch@adelphi.edu" target="_blank">sbloch@adelphi.edu</a><br><br></font></blockquote></div><br></div></div></blockquote></div><br>