Blog: 2024-02-12

Started on this quest to have a scheme repl where the outputs are italicized, like the SICP book.

Printing italics is pretty easy:

In [1]: line = 'a'

In [2]: print(f'\x1B[3m{line}\x1B[0m')
a

It's italic, trust me!

But when it comes to spawning a scheme subprocess and interacting with its stdin and stdout, I took many turns, eventually trying nodejs since its asynchronous io model more closely fits this use case.

Here's what worked (or at least is a work in progress)

(basically just a copy from the docs of https://www.npmjs.com/package/node-pty which it uses)

var pty = require('node-pty');

var ptyProcess = pty.spawn('scheme')

ptyProcess.onData((data) => {
    process.stdout.write(data);
});

ptyProcess.write('(+ 3 3)\r');

hack $ node scheme_pty.js
(+ 3 3)
Could not open file init.scm
TinyScheme 1.41
ts> 6
ts>

This also sorta works, but right now only processes the stdin with it being ended:

var spawn = require('child_process').spawn

scheme = spawn('scheme')

scheme.stdout.on('data', data => {
  console.log('data')
  console.log(data.toString())
  console.log()
})

scheme.stderr.on('data', data => {
  console.log('err')
  console.log(data.toString())
  console.log()
})

// setTimeout(() => {
  scheme.stdin.write('(+ 3 3)\r')
  // scheme.stdin.write('3\r\n')
  scheme.stdin.end()
// }, 500)

// scheme

// setInterval(() => {}, 1000)

What a mess... I didn't even get python working.. though it has pty built in so it probably would work