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This is a simple variant on write-only-1|: Instead of routing coprocess output directly to the output stream of the current job, we route it to the input stream, so that it gets processed by the current interpreter.

In muq/srv/ create a file write-only-2 with contents

select( (select(STDOUT), $| = 1)[0]);
for (;;) {
    printf "\"Loop %d\\n\" ,\n", $loop++;
    sleep 10;

As before, at the unix level, do chmod +x write-only-2 to make the script executable.

Now, at the Muq prompt do:

makeSocket --> s    @$s.standardInput$s.twin --> s$s.standardOutput
[ :socket s :commandline "write-only-2|" | ]rootPopenSocket

You will see a sequence of lines

Loop 0
Loop 1

printing out, one every ten seconds, but this time they result from the execution by the MUF interpreter of a series of lines

"Loop 0\n" ,
"Loop 1\n" ,

read from the coprocess. (Since the MUF interpreter prints a new prompt after each command executed, this time you see a prompt printed after each "Loop" line.)

As before, you may close down the subprocess by doing

[ :socket s | ]closeSocket

Gory Detail:

In the example, we use @$s.standardInput$s.twin rather that just @$s.standardInput because in general @$s.standardInput and @$s.standardOutput may be equal, both pointing to the same bidirectional stream. (This is virtually required by the CommonLisp standard in the simple case, since @$S.terminalIo must be bidirectional, and must be used by @$s.standardInput and @$s.standardOutput.)

Because Muq implements bidirectional streams using two unidirectional streams, and always indirecting all reads through stream$s.twin (which points to the stream itself in unidirectional streams), @$s.standardInput$s.twin gives us the stream which, when written, is guaranteed to deliver input to the current job.

If this is confusing, just remember that writing to @$s.standardInput$s.twin will always send input to the current job, whether it is using bidirection or unidirectional message streams.

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