scheme - how to do a count in RACKET -

i'm trying write code in racket , know how solve i'm having trouble , can use .

the function list , specific symbol , , need return number of times symbol shown in list . in test - i'm comparing result number i'm asking , should return true if number same .

i've tried (if / cond / , tried acc ) - there missing .

here code including test . please me find out how write .

the idea of solution , take head of list , check if it's equal symbol wrote , if - n plus 1 , empty list equal 0 .

( : counts : (listof symbol) -> integer )      (define (counts n )  ; = list of symbols.       (cond [(null? a) 0])         [(eq?(first a) 'x) (= n(+ n 1))]               (counts( (rest a) n)))      ;test:     (test (eq? (counts ('a 'b 'x) )1)) 

there several problems code:

• the cond expression being incorrectly used, , else case missing
• there erroneous parentheses, example @ end of second line in counts , when call counts in fourth line
• in base case of recursion must return n, counter
• you must call recursion if symbol found, in second case
• this part: (= n (+ n 1)) not doing think, it's not changing value of n, instead testing equality between n , (+ n 1) (which return false, of course)
• you're not passing parameter symbol being searched, it's hard-coded in procedure

this corrected version of intended write:

(define (counts x n)   (cond [(null? a) n]         [(eq? (first a) x)          (counts (rest a) x (+ n 1))]         [else          (counts (rest a) x n)])) 

use this:

(counts '(a b x c d x e x) 'x 0) => 3 

i advice grab book or tutorial, seems you're struggling basic syntax. , learn how use drracket syntax errors, it's excellent ide.