step0.js

const readline = require('readline');

function READ(x) {
  return x;
}

function EVAL(x) {
  return x;
}

function PRINT(x) {
  return x;
}

function rep(x) {
  return PRINT(EVAL(READ(x)));
}


const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  prompt: 'user> '
});

rl.prompt();

rl.on('line', (input) => {
  const result = rep(input);
  console.log(result);

  rl.prompt();
});

@markx regarding your query on #mal: Try setting readline.createInterface(... "terminal": false) otherwise it messes with the ability of the runtest script to test it. Also you might want that configurable because for normal interactive usage turning off terminal mode is annoying (no line editing or history). The node readline module is slightly screwy with regards to tty handling.