[plt-scheme] Doubt about hashes

From: ebellani at gmail.com (ebellani at gmail.com)
Date: Tue Nov 10 13:39:58 EST 2009

Hey Plt folk

I'm having a bit of a equality problem here, if someone
could help I would very much appreciate it:

;; build-lexical-analysis : string -> hash
;; calculates the letter frequency for a given word
;; uses the letter as key and the frequency as value for
;; a hash
(define (build-lexical-analysis word0)
  (local [(define (build-it word the-analysis)
              [(empty? word) the-analysis]
              [(hash-has-key? the-analysis
                              (first word))
               (build-it (rest word)
                (rest word)
                (hash-set the-analysis
                          (first word)
                          (count (λ (the-char)
                                   (equal? (first word)
    (build-it (string->list word0) #hash())))

(check-expect (build-lexical-analysis "hellol")
              #hash(("e" . 1)
                        ("h" . 1)
                        ("l" . 3)
                        ("o" . 1)))

Now, why is this check-expect failing? 

Eduardo Bellani


I object to doing things that computers can do.
- Olin Shivers

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