Difference between pipes and ports

[Zelphir Kaltstahl]

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

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repositories: https://notabug.org/ZelphirKaltstahl