On Wed, May 26, 2010 at 10:32 AM, Carl Eastlund <c...@ccs.neu.edu> wrote: > On Wed, May 26, 2010 at 10:27 AM, Matthias Felleisen > <matth...@ccs.neu.edu> wrote: >> >> On May 25, 2010, at 8:48 PM, Matthew Flatt wrote: >> >>> #lang racket >>> ;; Report each unique line from stdin: >>> (let ([saw (make-hash)]) >>> (for ([line (in-lines)]) >>> (unless (hash-ref saw line #f) >>> (displayln line)) >>> (hash-set! saw line #t))) >> >> I would prefer to sacrifice one line to avoid the repetition of the test >> (leakage). I doubt Perl and friends do that: >> >> #lang racket >> ;; Report each unique line from stdin: >> (define saw (make-hash)) >> (for ([line (in-lines)]) >> (hash-ref saw line >> (lambda () >> (displayln line) >> (hash-set! saw line #t)))) > > To anyone who isn't intimately familiar with hash-ref, both versions > are kind of obscure; the second one more so. If you insist on the > second one, though, use a lambda character and put the displayln on > the same line and you'll be back to 7. Personally, I'd recommend a > variant of the first that uses hash-has-key? instead of hash-ref. > It'll be much more readable.
And I would recommend using hash-ref! to save a line. Jay -- Jay McCarthy <j...@cs.byu.edu> Assistant Professor / Brigham Young University http://teammccarthy.org/jay "The glory of God is Intelligence" - D&C 93 _________________________________________________ For list-related administrative tasks: http://list.cs.brown.edu/mailman/listinfo/plt-dev
