It seems to me that the Design Recipe should come into play. Try to think what's the relation between the solution for a list of length n and one of length n-1.
[]s On 2011-05-30, Matthias Felleisen <matth...@ccs.neu.edu> wrote: > > On May 30, 2011, at 7:17 PM, Yingjian Ma wrote: > >> Hi All, >> >> I wrote a piece of code to count the occurrance of a letter in a list. >> But it gave me an error saying "#<procedure:...uments..." >> >> The code is below: >> >> (define (count-matches s l) >> (cond >> [(empty? l) 0] >> [(equal? s (first l)) (lambda (i)(+ i 1))] > > What's this lambda doing here? > > >> [else (count-matches s (rest l))])) >> >> Where the s is a letter and l is a list. To use it as an example, I typed >> >> (count-matches 'f '(f )) >> >> and got the error. The right result should be 1. >> >> Do I need to initialize i? If so, how can I do it? >> >> Note that the keywords that I can use are pretty much used in the code. >> If the solution needs keywords outside this post, it may not be useful to >> me. >> >> Thank you very much. >> _________________________________________________ >> For list-related administrative tasks: >> http://lists.racket-lang.org/listinfo/dev > > > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/dev > -- Sent from my mobile device Rodolfo Carvalho _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
