On Apr 3, 2014, at 7:08 PM, Spencer Florence <[email protected]> wrote:
> Is there any way to perform `substring` without creating a new string? I'm
> working with lots of very large and (for all intents and purposes) immutable
> strings and would like to avoid the extra allocations and copy time.
Seems like it would be fairly easy to roll this yourself:
#lang racket
(require rackunit)
;; represent a lazy substring operation:
(struct lazysubstring (str start end))
;; force a lazy substring
(define (lss-force s)
(substring (lazysubstring-str s)
(lazysubstring-start s)
(lazysubstring-end s)))
;; get the length of a lazy substring:
(define (lss-len s)
(- (lazysubstring-end s) (lazysubstring-start s)))
;; create one:
(define source-text "othho tot stnh ontuh .nt")
(define lss1 (lazysubstring source-text 3 9))
(check-equal? (lss-len lss1) 6)
Obviously, you have to “roll your own” for any operation that you want to
perform that retains the laziness.
John
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