Virtual Programming Lab (plugin)

Hi Andrew and Garth,

Thank you for your detailed message and for testing VPL with R on the Docker-based jail server. I’ve tried to reproduce your issue using the Docker image jcrodriguezvpl/jail-ubuntu-full, but so far, I haven’t encountered the same problem.

The message you're seeing — Error constructing proxy for org.gnome.Terminal — appears to be related not to VPL itself, but to the container’s graphical environment or its resource constraints.

Running R in VPL 4.3.2

With the release of VPL 4.3.2, we have simplified R integration by using VPL’s new running modes. These allow better control over how R scripts are executed, especially in text mode or GUI terminal environments.

As you may know, the R tool is based on a REPL (Read-Eval-Print Loop) interface, which complicates direct integration with VPL. After exploring various approaches, the latest solution uses Rscript, which is better suited for automated/scripted execution.

Here's how R execution works using Rscript in VPL 4.3.2:

• The first .R file in the student submission is run using Rscript --vanilla.

• Since Rscript is not interactive, you need to:

  • Use readLines(file("stdin"), n = 1) to read input.
  • To display charts:

  Save them as image files using png("file.png") or jpeg("file.jpg"). Generate the image, chart, etc. Close the graphics device using dev.off(). Show the image with an external viewer using:

  r system("nohup xdg-open file.png &")

  (Note: This need a text in GUI run mode)

Suggested Setup (if not using VPL 4.3.2)

If you're not yet on VPL 4.3.2, you can configure R execution manually by using the following vpl_run.sh script in "execution files" for text-only mode:

#!/bin/bash
# Script for running R in VPL
. common_script.sh
check_program R
get_first_source_file r R
cat common_script.sh > vpl_execution
echo "Rscript --vanilla \"$FIRST_SOURCE_FILE\"" >> vpl_execution
chmod +x vpl_execution

To run in a GUI terminal (text in GUI mode), you may add to the previous vpl_run.sh:

mv vpl_execution vpl_execution_in_gui
cat common_script.sh > vpl_wexecution
cat <<'END_SCRIPT' >> vpl_wexecution
if command -v gnome-terminal &> /dev/null; then
    gnome-terminal -- bash -c "./vpl_execution_in_gui; echo; read -p 'Press Enter to continue...'"
elif command -v xterm &> /dev/null; then
    xterm -e bash -c "./vpl_execution_in_gui; echo; read -p 'Press Enter to continue...'"
elif command -v konsole &> /dev/null; then
    konsole --noclose -e "./vpl_execution_in_gui"
elif command -v xfce4-terminal &> /dev/null; then
    xfce4-terminal --hold --command="./vpl_execution_in_gui"
else
    echo "No terminal emulator found. Running without GUI terminal."
    ./vpl_execution_in_gui
fi
wait_end vpl_execution_in_gui
END_SCRIPT
chmod +x vpl_wexecution

Best regards, Juan Carlos Rodríguez