Re: [Sbcl-devel] new line character in the string when using read-line with stream with \r\n line endings

[Dmitry I. <dfi...@gm...>]

2016-01-25 20:50 GMT+03:00 Jeff Cunningham <je...@jk...>:

> On 01/25/2016 06:47 AM, Stas Boukarev wrote:
> > On Mon, Jan 25, 2016 at 5:37 PM, Jeff Cunningham
> > <je...@jk...> wrote:
> >>
> >> On 01/24/2016 10:47 PM, Krzysztof Wicher wrote:
> >>> Hi guys,
> >>>
> >>> I literally just started with common lisp and I believe I might've
> >>> encountered a bug in sbcl.
> >>>
> >>> Simple example:
> >>> (loop for c across (read-line (make-string-input-stream "aaa
> >>> aaa")) do (format t "~a~%" (char-code c)))
> >>>
> >>> output when using CRLF line endings:
> >>> 97
> >>> 97
> >>> 97
> >>> 13
> >>>
> >>> output when using linux line endings:
> >>> 97
> >>> 97
> >>> 97
> >>>
> >>>
> >>> this is causing simple programs as this (solution to:
> >>> http://www.spoj.com/problems/TEST/ ):
> >>> (loop
> >>>      (let
> >>>          ((line (read-line)))
> >>>          (if (equal line "42") (return))
> >>>          (format t "~a~%" line)))
> >>>
> >>> not pass locally on Windows command prompt while passing on the server
> >>> (this is how I found this bug)
> >>>
> >>> I'm running SBCL 1.3.1
> >>> with:
> >>> sbcl --script test.lisp
> >>>
> >>> Cheers,
> >>> Krzysztof
> >>
> >> The link problem doesn't say anything about reading from a text list
> >> which just adds complexity. This will do what they asked:
> >>
> >> (loop for c in (list 1 2 88 42 99) until (= c 42)
> >>      do (print c))
> >>
> >> Most of the time CR/LF's are a non-issue - an indication you're
> >> approaching the problem wrong.  For example, read eats whitespace -
> >> including CR - just fine. You don't need to use readline for this
> problem:
> >>
> >> (let ((is (make-string-input-stream "1
> >> 2
> >> 88
> >> 42
> >> 99")))
> >>     (do ((v (read is nil nil) (read is nil nil)))
> >>         ((or (null v) (= v 42)))
> >>       (print v)))
> >>
> >> Or if you want it in a loop construct:
> >>
> >> (let ((is (make-string-input-stream "1
> >> 2
> >> 88
> >> 42
> >> 99")))
> >>     (loop (let ((v (read is nil nil)))
> >>             (when (or (null v) (= v 42)) (return))
> >>             (print v))))
> >>
> >> CL-USER>
> >> ; No value; compiling (LET (#) ...)
> >> 1
> >> 2
> >> 88
> > Using READ for reading stuff that is not lisp source code is a really
> > bad idea. Never do it.
>
> Why?
>
Because "read parses the printed representation of an object" (CLHS), while
read-line just "reads from input-stream a line of text that is terminated
by a newline
or end of file". read-line is a low-level function that just reads from the
stream
without any parsing and just returns string rather then Lisp datum.