[plt-scheme] critique of some code

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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>
>