From Newsgroup: comp.lang.postscript

One thing lacking in PostScript is good foreign function interface. There
is %pipe% (specific to Ghostscript, but I had made a list of my own ideas
of a new version of PostScript, and this is one of them), but the pipe is
only one direction of data at a time; it is not two way pipe.

There is printobject/writeobject (reading this format can be implemented
in a not too long C code, which I had posted to this newsgroup before), although it has some limitations.
--
Don't laugh at the moon when it is day time in France.
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From Newsgroup: comp.lang.postscript

One thing lacking in PostScript is good foreign function interface. There
is %pipe% (specific to Ghostscript, but I had made a list of my own ideas
of a new version of PostScript, and this is one of them), but the pipe is only one direction of data at a time; it is not two way pipe.

Much of the functionality of a two-way pipe can be implemented
on any OS that provides named pipes. Use an anonymous %pipe%
for the output from PostScript into the input of the external pipeline,
and write the output of the pipeline into a named pipe that is
consumed by open+read.
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