;; functions that check types
(number? -0.98)
(number? (+ 4 -77))
(number? 4/3)

(integer? 3.14)
(real? 3.14)
(integer? 8/2)

(exact? 3.14)
(exact? 8/2)
(exact? 1/3)
(exact? (sin 5))
(exact? (ceiling (sin 5)))

(boolean? true)
(boolean? 'true)

(symbol? 'yes)
(symbol? 5)
(symbol? "yes")

;; using type checks in functions
;; Contract: number -> number (or symbol on error)

;; Purpose: to compute the square root of the cube
;; of a number. If the parameter is not a number or 
;; is negative returns a symbol to signal an error
(define (sqrt-of-cube x)
 (cond
   [(not (number? x)) 'NotANumber]
   [(< x 0) 'NoRootOfNegativeNumber]
   [else (sqrt (* x x x))]
 )
)

(check-expect (sqrt-of-cube "banana") 'NotANumber)