[plt-scheme] critique of some code

Alternatively, 

#lang scheme

(require test-engine/scheme-tests)

(define (string-index-of str sub)
  [define l1 (string-length str)]
  [define l2 (string-length sub)]
  (or (for/first ((i (in-range (- l1 l2 -1))) 
                  #:when (string=? (substring str i (+ i l2)) sub))
        i)
      -1))

(check-expect (string-index-of "abcd" "a") 0)
(check-expect (string-index-of "abc" "bc") 1)
(check-expect (string-index-of "abcd" "d") 3)
(check-expect (string-index-of "abcd" "de") -1)
(check-expect (string-index-of "abcd" "abcde") -1)

(test)


On Dec 6, 2009, at 10:31 PM, Matthias Felleisen wrote:

> 
> Why not use regexp-match-positions? 
> 
> On Dec 6, 2009, at 10:27 PM, Todd O'Bryan wrote:
> 
>> I still think imperatively, but I'm working on it.
>> 
>> I just wrote the equivalent of Java's String indexOf() method and am
>> wondering if I got something that a Schemer would be satisfied with.
>> 
>> Here's the code, with tests:
>> 
>> (define (string-index-of str sub)
>> (let ([l1 (string-length str)]
>>       [l2 (string-length sub)])
>>   (or (and (>= l1 l2)
>>            (ormap
>>             (lambda (start)
>>               (if (string=? (substring str start (+ start l2))
>>                             sub)
>>                   start
>>                   #f))
>>             (build-list (add1 (- l1 l2)) (lambda (x) x))))
>>       -1)))
>> 
>> (check-expect (string-index-of "abcd" "a") 0)
>> (check-expect (string-index-of "abc" "bc") 1)
>> (check-expect (string-index-of "abcd" "d") 3)
>> (check-expect (string-index-of "abcd" "de") -1)
>> (check-expect (string-index-of "abcd" "abcde") -1)
>> 
>> Did I miss something that would have made this clearer or more succinct?
>> 
>> Todd
>> _________________________________________________
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> 
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