(define-struct student (first last major)) (define student1 (make-student "John" "Smith" 'CS)) (define student2 (make-student"Jane" "Jones" 'Math)) (define student3 (make-student "Jim" "Black" 'CS)) #;(define (same-major? s1 s2) (symbol=? (student-major s1) (student-major s2))) when I type these in, I get the answer I expect.
;;(same-major? student1 student2) -> FALSE ;;(same-mejor? student1 student3) -> True But when I want to find out if the students have the same first name, it tells me that they expect a symbol as a 1st argument, but given John.
(define (same-first? s1 s2) (symbol=? (student-first s1) (student-first s2))) What am I doing wrong?
2 Answers
'CS and 'Math are symbols, "John", "Jane" and "Jim" are not (they're strings). As the error message is telling you, the arguments to symbol=? need to be symbols.
To compare strings for equality, you can use string=? or just equal? (which works with strings, symbols and pretty much everything else).
Change this:
(symbol=? (student-major s1) (student-major s2))) To this:
(string=? (student-major s1) (student-major s2))) Notice that you're comparing strings not symbols, so the appropriate equality procedure must be used.
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