[plt-scheme] Processing lists

From: aditya shukla (adityashukla1983 at gmail.com)
Date: Thu Mar 5 19:13:03 EST 2009

i am trying to solve a problem which is to find out number of occurrence of
a symbol in list of symbols.

;question in a given list find out how many times  a symbol occurs in the
;contract : fun-with-lists s-list * symbol -> number
;purpose : this function takes an s-list and a symbol as input and finds out
how many times the symbol occurs in the list.
;examples 'a -> () =0 , ('a) =1 , ('b) = 0 , ('b 'c 'a 'a) = 2 , ('b 'c 'd)
;template (define fun-with-lists (lambda s-list sym) (cond [(empty? s-list)]
[ else (first s-list) fun-with-lists(rest s-list])))
(define fun-with-lists (lambda (s-list sym )
                           [(empty? s-list) 0]
                           [else (cond
                                   [(symbol=? (first s-list) sym ) 1]

                                   [else (fun-with-lists (rest s-list) sym

I got to this far using the recipe explained in htdp.I am stuck at the point
where i can't increment the occurrence of a symbol .Can someone give me a

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