[plt-scheme] critique of some code

Yuck. Yuck. Yuck. Back to work. 

On Dec 6, 2009, at 11:20 PM, Shriram Krishnamurthi wrote:

> You put your types in comments and cond's outside, I put my cond's in
> comments and types outside.  We're even.
> 
> Shriram
> 
> On Sun, Dec 6, 2009 at 11:14 PM, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
>> 
>> uh, oh, I hate and/or nests? Does this make me a non-Schemer?
>> 
>> On Dec 6, 2009, at 11:05 PM, Shriram Krishnamurthi wrote:
>> 
>>> Here's my version.
>>> 
>>> Zero, I assume you want the naive version, not something like the KMP
>>> or BM algorithms.
>>> 
>>> First, I changed your contract to return false instead of -1, because
>>> that's what a Schemer would have done.
>>> 
>>> Second, I converted to lists, because that's also what a Schemer would
>>> do (unless you were concerned about long strings, in which case anyway
>>> you'd use KMP/BM above some threshold).
>>> 
>>> Third, here's both the and/or version and the cond version.
>>> 
>>> Fourth, it's in TS.
>>> 
>>> S.
>>> 
>>> ----------------------------------------------------------------------
>>> #lang typed-scheme
>>> 
>>> (require scheme/list)
>>> (require scheme/bool)
>>> 
>>> (: string-index-of (String String -> (U Number Boolean)))
>>> 
>>> (define (string-index-of in for)
>>>  (sio/list (string->list in) (string->list for) 0))
>>> 
>>> (define: (sio/list [check-in : (Listof Char)]
>>>                   [check-for : (Listof Char)]
>>>                   [index : Number]) : (U Number Boolean)
>>>  (and (not (empty? check-in))
>>>       (or (and (prefix-of? check-for check-in) index)
>>>           (sio/list (rest check-in) check-for (add1 index)))))
>>> #|
>>>  (cond
>>>    [(empty? check-in) false]
>>>    [else (if (prefix-of? check-for check-in)
>>>              index
>>>              (sio/list (rest check-in) check-for (add1 index)))]))
>>> |#
>>> 
>>> (define: (prefix-of? [pre : (Listof Char)]
>>>                     [big : (Listof Char)]) : Boolean
>>>  (or (empty? pre)
>>>      (and (not (empty? big))
>>>           (char=? (first pre) (first big))
>>>           (prefix-of? (rest pre) (rest big)))))
>>> #|
>>>  (cond
>>>    [(empty? pre) true]
>>>    [(empty? big) false]
>>>    [else (and (char=? (first pre) (first big))
>>>               (prefix-of? (rest pre) (rest big)))]))
>>> |#
>>> 
>>> (define check-expect equal?)
>>> (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") false)
>>> (check-expect (string-index-of "abcd" "abcde") false)
>>> ----------------------------------------------------------------------
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>> 
>>