;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname union-of-struct-example) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
#|
A Glarp is:
 - a number, OR
 - "hmmm", OR
 - (make-blah [string] [boolean] [Glarp])


* Give 4 examples
* give template
* write `foo : Glarp -> natnum`,
  returns the # of 'm's in the given Glarp
|#

(define-struct blah (name happy? owner))

; examples of the data

17
"hmmm"
(make-blah "rover" #true "hmmm")
(make-blah "fido" #false (make-blah "rover" #true "hmmm"))

; template

; func-for-Glarp : Glarp -> ??
;
(define (func-for-glarp a-g)
  (cond [(number? a-g) ...]
        [(string? a-g) ...]
        [(blah? a-g)   (... (blah-name a-g)
                        ... (blah-happy? a-g)
                        ... (func-for-glarp (blah-owner a-g)))]))


(check-expect (foo 17) 0)
(check-expect (foo "hmmm") 3)
(check-expect (foo (make-blah "rover" #true "hmmm")) 3)
(check-expect (foo (make-blah "fido" #false (make-blah "rover" #true "hmmm"))) 3)
(check-expect (foo (make-blah "daisy" #true (make-blah "fido" #false (make-blah "rover" #true "hmmm")))) 3)
(check-expect (foo (make-blah "daisy" #true (make-blah "jemal" #false (make-blah "jimmmy" #true "hmmm")))) 7)

;  foo : Glarp -> natnum
;  returns the # of 'm's in the given Glarp
(define (foo a-g)
  (cond [(number? a-g) 0]
        [(string? a-g) 3]
        [(blah? a-g)   (+ (count-ms (blah-name a-g))
                          (foo (blah-owner a-g)))]))

(define (count-ms str)
  (length (filter is-m? (string->list str))))

(define (is-m? c) (char=? #\m c))