;; Examples of errors 

;; what's the problem? 
;; when is it detected? Two types of error:
;; syntax error (detected before the program runs)
;; run-time errors (detected when an attempt to execute
;; an operation fails.
;; When there is a syntax error, the evaluation is 
;; not attepmpted. Run-time error means that the evaluation
;; is attempted and fails. 

(+ (2 3)) ; syntax error: 2 is a number, not a function name

;(2 sqrt)  ; syntax error: 2 is a number, not a function name

;(srt 2)  ; syntax error: unknown function srt

;(/ 2 0) ; run-time error: division by 0

;(/ 2 (- 5 (/ 10 2))) ; run-time error: division by 0

;(define (f n) (n n)) ; syntax error at Beginner Student level: unknown function name n

;(define (f n) (/ n (- n n))) ; this definition is syntactically correct. The function is not applied so its body is not executed

;(f 4) ; run-time error when the function is applied

;(f 2.5) ; run-time error when the function is applied

;(define (add7 n) (+ n 7)) ; correct definition

;(add7 "Hi there!") ; run-time error when + is applied to a string