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 <zelphirkaltst...@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 > > >