I was solving this exercise from htdp , its been quite some days since i wrote a program in scheme .I am getting this error which i am not able to sort out .Can someone please help me with this. ;data definition (define-struct child (father mother name date eyes)) ;oldest generation (define Carl (make-child empty empty 'Carl 1926 'green)) (define Bettina (make-child empty empty 'Bettina 1926 'green)) ;; Middle Generation: (define Adam (make-child Carl Bettina 'Adam 1950 'yellow)) (define Dave (make-child Carl Bettina 'Dave 1955 'black)) (define Eva (make-child Carl Bettina 'Eva 1965 'blue)) (define Fred (make-child empty empty 'Fred 1966 'pink)) ;; Youngest Generation: (define Gustav (make-child Fred Eva 'Gustav 1988 'brown)) ;A family-tree-node (short: ftn) is either ; 1. ; empty; or ;2. ; (make-child f m na da ec) ; where f and m are ftns, na ;and ec are symbols, and da is a number. ;contract of count-persons ftn(family tree node) -> number ;Purpose :This function takes a family tree node and computes the number of persons in that node ;examples empty -> 0 ,carl ->1 , bettina -> 1 , adam , dave , eva -> 3 , fred->1 , gustav-> 5 ;template(define count-persons (lambda (ftn) (cond [(empty? ftn )][else (count-persons (child-father ftn)) (count-persons (child-mother ftn)) (child-name ftn) (child-date ftn) (child-eyes ftn)]))) (define (count-persons a-ftree) (cond [(empty? a-ftree) 0] [else ((symbol? (child-name a-ftree)) (+ 1 (count-persons(or (child? (child-father a-ftree) ) (child? (child-mother a-ftree) )))))])) (count-persons Fred) function call: expected a name after an open parenthesis, but found something else Thanks, Aditya