racket - Scheme's "expected a procedure that can be applied to arguments" -

i use drracket. have problem code:

          (define (qweqwe n) (                       (cond                          [(< n 10) #t]                         [(>= (lastnum n) (pochtilastnum n)) (qweqwe (quotient n 10))]                         [else #f]                         )                       )     )     (define ( rty file1 file2 )       (define out (open-output-file file2 #:mode  'text #:exists 'replace))       (define in (open-input-file file1))      (define (printtofile q) (begin                    (write q out)                    (display '#\newline out)                    ))        (define (next)            (define n (read in))  (cond        [(equal? n eof) #t]       [else (begin       ((if (qweqwe n) (printtofile n) #f))       ) (next)]       ) )     (next)       (close-input-port in)    (close-output-port out))  

but when start ( rty "in.txt" "out.txt" ) have error @ ((if (qweqwe n) (printtofile n) #f)) :

    application: not procedure;     expected procedure can applied arguments     given: #f     arguments...: [none] 

what's problem?

add: changedmy code to:

(cond        [(equal? n eof) #t]       [else       (if (qweqwe n) (printtofile n) #f)       (next)]       ) 

but problem remains.

there unnecessary parenthesis, don't this:

((if (qweqwe n) (printtofile n) #f)) 

try instead:

(if (qweqwe n) (printtofile n) #f) 

also in here:

(define (qweqwe n)   ((cond [(< n 10) #t]          [(>= (lastnum n) (pochtilastnum n)) (qweqwe (quotient n 10))]          [else #f]))) 

it should be:

(define (qweqwe n)   (cond [(< n 10) #t]         [(>= (lastnum n) (pochtilastnum n)) (qweqwe (quotient n 10))]         [else #f])) 

in both cases problem if surround () expression, means you're trying invoke procedure. , given result of if , cond expressions above don't return procedure, error occurs. also, bothbegins in original code unnecessary, cond has implicit begin after each condition, same thing body of procedure definition.