open-pipe* seems to buffer all of my writes when I don't want it.

[Tim Meehan <btmeehan@gmail.com>]

I was trying to use Matplotlib to plot some data, through a call to
"open-pipe*" ... I'm trying to slowly rewrite some of my tools in Scheme.

When I run the program from the shell with "python -i plotter.py" I can
send it updates ... but when I run it through Guile, it seems to store up
all of my updates, then right before the program closes a window pops up
for a fraction of a second and then vanishes. Am I using "open-pipe*"
incorrectly?

#!/usr/bin/guile
!#

(use-modules (ice-9 popen)
             (ice-9 readline)
             (ice-9 textual-ports))

(define program (string-concatenate
    '("import scipy.special\n"
      "import matplotlib.pyplot as plt\n"
      "import numpy as np\n"

      "x  = np.linspace(0, 10)\n"
      "y0 = scipy.special.jv(0, x)\n"

      "def update_data():\n"
      "    print('updating')\n"
      "    noise = np.random.randn(y0.size)*0.1\n"
      "    line1.set_ydata(y0 + noise)\n"
      "    plt.pause(0.1)\n"

      "fig, ax = plt.subplots(1, 2)\n"
      "ax[0].plot(x, y0)\n"
      "ax[0].set_title('Original Data')\n"
      "ax[0].set_xlabel('X')\n"
      "ax[0].set_ylabel('Y')\n"

      "ax[1].plot(x, y0)\n"
      "line1, = ax[1].plot(x, y0, '.')\n"
      "ax[1].set_title('Noisy Data')\n"
      "ax[1].set_xlabel('X')\n"
      "ax[1].set_ylabel('Y')\n"
      "fig.show()\n"
      "plt.pause(0.1)\n")))


(define prompt "update? ('quit' to stop')")
(define stuff (open-pipe* OPEN_WRITE "python3"))
(setvbuf stuff 'none)

(put-string stuff program)
(force-output stuff)

(let loop ([command (readline prompt)])
    (unless (string-prefix? "quit" command)
        (display "updating\n")
        (put-string stuff "update_data()\n")
        (loop (readline prompt))))

(close-pipe stuff)