It seems your input data is not right here. I use your code (see below), it
works well (besides the overflow problem).
#lang racket
;it is list operation though parameter is str
;as little like human, check first and last character first
(define count 0)
(define data (string->list "explorers"))
(define (search str)
(set! count 0)
(define len (length str))
(define data-len (length data))
(when (and (not (= 0 len)) (>= data-len len))
(define first-char (first str))
(define last-char (last str))
;is it exactly same?
(define (exact? str len index)
(newline)
(display str)
(newline)
(display (drop (take data (+ index len)) index))
(newline)
(if (equal? str (drop (take data (+ index len)) index))
#t
#f))
;if first and last character is correct, then compare whole searching
string, if not, skip
(define (loop [index 0])
(when (> data-len index)
(if (and (equal? first-char (list-ref data index))
(display index)
(newline)
(display len)
(newline)
(display "==================")
(equal? last-char (list-ref data (+ index len -1))))
(when (exact? str len index)
(set! count (+ count 1))
(loop (+ index len)))
(loop (+ index 1)))))
(loop))
(format "Found ~a" count))
(search (string->list "explorer"))
On 20 May 2011 17:51, Nevo <sakur.dea...@gmail.com> wrote:
> A quick look.
> You're not guarding the list end ( (+ index len - 1) should be also less
> than data-len), that's why you have index overflow error. Then when you
> tried to search "2explorer" from "2explorers", the first turn of loop
> failed, then the second turn of loop failed on "(equal? first-char (list-ref
> data index))", that's why you cannot find "2explorer".
>
>
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