* Difference between pipes and ports
@ 2021-08-11 1:14 Zelphir Kaltstahl
2021-08-11 3:16 ` Mikael Djurfeldt
0 siblings, 1 reply; 3+ messages in thread
From: Zelphir Kaltstahl @ 2021-08-11 1:14 UTC (permalink / raw)
To: guile-user
Hello Guile users,
I recently came across
https://www.draketo.de/software/guile-capture-stdout-stderr.html
<https://www.draketo.de/software/guile-capture-stdout-stderr.html> and wrote a
commented version at
https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm
<https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm>.
While looking at the code, I was starting to wonder, what the difference between
a pipe and a port is. The reference manual does not say much about any
definition of what a pipe is at
https://www.gnu.org/software/guile/manual/html_node/Pipes.html
<https://www.gnu.org/software/guile/manual/html_node/Pipes.html> and pipe
procedure return values are also named port.
However, in the REPL, they look not the same:
~~~~
scheme@(guile-user)> (import (ice-9 popen))
scheme@(guile-user)> (open-input-pipe "ls -al")
$2 = #<input: #{read pipe}# 13>
~~~~
And here for ports:
~~~~
scheme@(guile-user)> (call-with-output-string
(λ (port)
(display port)))
#<output: file 7fa2a99471c0>$6 = ""
~~~~
Is a pipe just a special kind of port? Does it wrap a port? Or is it perhaps
merely a different terminology used in different contexts in the reference manual?
Best regards,
Zelphir
--
repositories: https://notabug.org/ZelphirKaltstahl
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Difference between pipes and ports
2021-08-11 1:14 Difference between pipes and ports Zelphir Kaltstahl
@ 2021-08-11 3:16 ` Mikael Djurfeldt
2021-08-11 9:48 ` Zelphir Kaltstahl
0 siblings, 1 reply; 3+ messages in thread
From: Mikael Djurfeldt @ 2021-08-11 3:16 UTC (permalink / raw)
To: Zelphir Kaltstahl; +Cc: guile-user
Hi Zelphir!
A port is a scheme level concept which represents input and output devices.
Stdin, stdout and stderr are file descriptors which is an OS level concept.
A pipe is also an OS level concept. It is a communication stream between
two processes. In the OS, it is represented as a file descriptor once
opened.
The function open-input-pipe creates a child process and opens a pipe from
it. In the OS, the pipe is represented as a file descriptor. This is
represented as a port at the scheme level.
In Guile, this port also has some extra information: It has a type, #{read
pipe}, and also carries (i believe) some extra information, such as the
process identifier of the child process.
Best regards,
Mikael
Den ons 11 aug. 2021 03:14Zelphir Kaltstahl <zelphirkaltstahl@posteo.de>
skrev:
> Hello Guile users,
>
> I recently came across
> https://www.draketo.de/software/guile-capture-stdout-stderr.html
> <https://www.draketo.de/software/guile-capture-stdout-stderr.html> and
> wrote a
> commented version at
>
> https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm
> <
> https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm
> >.
>
> While looking at the code, I was starting to wonder, what the difference
> between
> a pipe and a port is. The reference manual does not say much about any
> definition of what a pipe is at
> https://www.gnu.org/software/guile/manual/html_node/Pipes.html
> <https://www.gnu.org/software/guile/manual/html_node/Pipes.html> and pipe
> procedure return values are also named port.
>
> However, in the REPL, they look not the same:
>
> ~~~~
> scheme@(guile-user)> (import (ice-9 popen))
> scheme@(guile-user)> (open-input-pipe "ls -al")
> $2 = #<input: #{read pipe}# 13>
> ~~~~
>
> And here for ports:
>
> ~~~~
> scheme@(guile-user)> (call-with-output-string
> (λ (port)
> (display port)))
> #<output: file 7fa2a99471c0>$6 = ""
> ~~~~
>
> Is a pipe just a special kind of port? Does it wrap a port? Or is it
> perhaps
> merely a different terminology used in different contexts in the reference
> manual?
>
> Best regards,
> Zelphir
>
> --
> repositories: https://notabug.org/ZelphirKaltstahl
>
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Difference between pipes and ports
2021-08-11 3:16 ` Mikael Djurfeldt
@ 2021-08-11 9:48 ` Zelphir Kaltstahl
0 siblings, 0 replies; 3+ messages in thread
From: Zelphir Kaltstahl @ 2021-08-11 9:48 UTC (permalink / raw)
To: mikael; +Cc: guile-user
Hello Mikael!
Thank you, that makes it clearer. Different levels of abstraction and pipes of
the OS level are represented as ports in Guile. I think I understand now. I
quite like the ports concept with its many uses.
Best regards,
Zelphir
On 8/11/21 5:16 AM, Mikael Djurfeldt wrote:
> Hi Zelphir!
>
> A port is a scheme level concept which represents input and output devices.
>
> Stdin, stdout and stderr are file descriptors which is an OS level concept.
>
> A pipe is also an OS level concept. It is a communication stream between two
> processes. In the OS, it is represented as a file descriptor once opened.
>
> The function open-input-pipe creates a child process and opens a pipe from it.
> In the OS, the pipe is represented as a file descriptor. This is represented
> as a port at the scheme level.
>
> In Guile, this port also has some extra information: It has a type, #{read
> pipe}, and also carries (i believe) some extra information, such as the
> process identifier of the child process.
>
> Best regards,
> Mikael
>
> Den ons 11 aug. 2021 03:14Zelphir Kaltstahl <zelphirkaltstahl@posteo.de
> <mailto:zelphirkaltstahl@posteo.de>> skrev:
>
> Hello Guile users,
>
> I recently came across
> https://www.draketo.de/software/guile-capture-stdout-stderr.html
> <https://www.draketo.de/software/guile-capture-stdout-stderr.html>
> <https://www.draketo.de/software/guile-capture-stdout-stderr.html
> <https://www.draketo.de/software/guile-capture-stdout-stderr.html>> and
> wrote a
> commented version at
> https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm
> <https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm>
> <https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm
> <https://notabug.org/ZelphirKaltstahl/guile-examples/src/master/input-output/stdout-stderr.scm>>.
>
> While looking at the code, I was starting to wonder, what the difference
> between
> a pipe and a port is. The reference manual does not say much about any
> definition of what a pipe is at
> https://www.gnu.org/software/guile/manual/html_node/Pipes.html
> <https://www.gnu.org/software/guile/manual/html_node/Pipes.html>
> <https://www.gnu.org/software/guile/manual/html_node/Pipes.html
> <https://www.gnu.org/software/guile/manual/html_node/Pipes.html>> and pipe
> procedure return values are also named port.
>
> However, in the REPL, they look not the same:
>
> ~~~~
> scheme@(guile-user)> (import (ice-9 popen))
> scheme@(guile-user)> (open-input-pipe "ls -al")
> $2 = #<input: #{read pipe}# 13>
> ~~~~
>
> And here for ports:
>
> ~~~~
> scheme@(guile-user)> (call-with-output-string
> (λ (port)
> (display port)))
> #<output: file 7fa2a99471c0>$6 = ""
> ~~~~
>
> Is a pipe just a special kind of port? Does it wrap a port? Or is it perhaps
> merely a different terminology used in different contexts in the reference
> manual?
>
> Best regards,
> Zelphir
>
> --
> repositories: https://notabug.org/ZelphirKaltstahl
> <https://notabug.org/ZelphirKaltstahl>
>
>
--
repositories: https://notabug.org/ZelphirKaltstahl
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-08-11 3:16 ` Mikael Djurfeldt
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