If I understand the docs correctly, the OS-specific handling is in
open-input-file, but it is not the default.
Here is an alternative to read-line that preserves line endings:
#lang racket/base
;; my-read-line : InputPort -> String
;; Like read-line, but preserves line ending.
;; Fails if port contains specials.
(define (my-read-line in [mode 'any])
(define rx
(case mode
[(any) #rx"^[^\n\r]*(?:\r\n|\n|\r|$)"]
[(linefeed) #rx"^[^\n]*(?:\n|$)"]
;; ...
[else (error 'my-read-line "unsupported mode: ~e" mode)]))
(define m (car (regexp-match rx in))) ;; rx accepts "", can't fail
(if (equal? m #"") eof (bytes->string/utf-8 m)))
(require rackunit racket/port)
(check-equal?
(port->list my-read-line (open-input-string "abc\ndef\r\ngh\n"))
'("abc\n" "def\r\n" "gh\n"))
(check-equal?
(port->list my-read-line (open-input-string "abc\ndef\r\ngh"))
'("abc\n" "def\r\n" "gh"))
(check-equal?
(port->list my-read-line (open-input-string "\n\r\n\n\r\r\n"))
'("\n" "\r\n" "\n" "\r" "\r\n"))
(check-equal?
(port->list (lambda (in) (my-read-line in 'linefeed))
(open-input-string "\n\r\n\n\r\r\n"))
'("\n" "\r\n" "\n" "\r\r\n"))
Ryan
On Thu, Jul 30, 2020 at 5:11 AM Shriram Krishnamurthi
wrote:
> Suppose I have two files that are identical, except one ends in a newline
> and the other does not. If I use `read-line` to read the successive lines
> of this file, because it swallows the line separators, there is no way to
> tell them apart. E.g., these two strings
>
> "a
> b"
>
> and
>
> "a
> b
> "
>
> read using `read-line` and `open-input-string` produce the same result.
>
> This is unfortunate for a program SPDEGabrielle has induced me to write
> (-:.
>
> Any reasonable ways to work around this that rely, as much as possible, on
> the OS-specific handling `read-line` already provides?
>
> Shriram
>
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