READ from terminal stdin blocks until end of file
David Banks
Using the following program 'reader.scm':
#!r6rs
(import (rnrs))
(let loop ()
(let ((datum (read)))
(write datum)
(newline)
(loop)))
I type in some numbers, followed by a newline each time.
amoe@glimworm $ mosh reader.scm
1
2
3
4
[I send EOF with ^D]
1
[^D]
2
[^D]
3
[^D]
4
[^D]
#<eof-object>
...etc.
As you can see the (read) call is blocking until it sees an EOF,
whereas I think it should return and write the result immediately,
like this:
amoe@glimworm $ mosh reader.scm
1
1 [from mosh]
2
2 [from mosh]
.... etc ...
Indeed that's the behaviour that I get from Ikarus and Ypsilon. I'm
not sure if this is a bug as it's probably technically unspecified.
But this behaviour seems quite surprising.
It seems this behaviour only happens at the terminal as it works fine
if I redirect stdin. (If it really had to receive 4 EOFs before
writing output it would presumably hang.)
Cheers,
--
David Banks <amo...@gmail.com>
okuoku
> Hi all,
- snip -
> As you can see the (read) call is blocking until it sees an EOF,
> whereas I think it should return and write the result immediately,
> like this:
Reading from terminal is quite un-portable thingy.. and mosh's READ is
optimized aggressively.
If your script requires (REPL like) input prompt, please avoid to use
READ directly and try followings:
1) - Use get-line and buffer input.
(import (rnrs))
(define (string->datum str)
(call-with-port (open-string-input-port str) read))
(define (readline)
(string->datum (get-line (current-input-port))))
(let loop ()
(let ((datum (readline)))
(write datum)
(newline)
(loop)))
2) - POSIX systems and Nmosh only
Recent Nmosh has terminal control functions, so you can enable
char-by-char input like this:
WARNING: you cannot stop this script by CTRL+C
(import (rnrs) (nmosh stubs terminal))
(when (terminal_isatty 0) ;; 0 means stdin
(display "IT'S A TTY!\n")
(terminal_acquire))
(let loop ()
(let ((datum (get-char (current-input-port))))
(write datum)
(newline)
(loop)))
(terminal_release)
I recommend 1) because it's portable (includes other R6RS
implementation) and work as excepted.
David Banks
> Reading from terminal is quite un-portable thingy.. and mosh's READ is
> optimized aggressively.
>
> If your script requires (REPL like) input prompt, please avoid to use
> READ directly and try followings:
>
> 1) - Use get-line and buffer input.
> I recommend 1) because it's portable (includes other R6RS
> implementation) and work as excepted.
ACK, I will do so. Thanks Okuoko.
--
David Banks <amo...@gmail.com>