pre-command-quizzes

## pre-command-quizzes
Check out this blog post for details: https://igliu.com/how-to-learn-a-natural-language/

## .zshrc
# ...

# Before all your aliases
alias ls="/usr/local/bin/precmd.js; ls"
alias cd="/usr/local/bin/precmd.js; cd"
alias git="/usr/local/bin/precmd.js; git"
# repeat with other non-urgent commands that you use often

# other aliases
# ...

# ...

## precmd.js
#! /usr/bin/node

// @author Anthony Liu <igliu@mit.edu>
// @date 2017-01-11

var fs = require('fs');
var readlineSync = require('readline-sync');

// config
var incidence = 0.2; // occurs with this probability
var questionsPerIncident = 5; // this many right answers per incident
var likelyRatio = 8; // easiest word is this much less likely
var dirName = '~~ LOCATION OF YOUR WORDS FILE ~~'; // directory that the data file is in
var fileName = 'words.txt'; //the name of the data file

// parses a file into a list of from->to pairs
function deserialize(fileLoc, callback) {
  fs.readFile(fileLoc, 'utf8', function(err, contents) {
    if (err) {
      return callback(err, false);
    }

    try {
      var data = [];
      var lines = contents.split('\n');
      lines.forEach(function(line) {
        if (line.length > 0) {
          var components = line.split(',');
          var from = components[0];
          var to = components[1];
          var correct = components.length == 4 ? components[2] : 0;
          var incorrect = components.length == 4 ? components[3] : 0;
          correct = parseInt(correct);
          incorrect = parseInt(incorrect);
          data.push({
            'from': from,
            'to': to,
            'correct': correct,
            'incorrect': incorrect
          });
        }
      });
      return callback(false, data);
    } catch (e) {
      console.log(e.message);
      return callback(true);
    }
  });
}

// converts a list of from->to pairs to a string
function serialize(data) {
  var str = '';
  for (var i = 0; i < data.length; i++) {
    var word = data[i];
    var line = word.from + ',';
    line += word.to + ',';
    line += word.correct + ',';
    line += word.incorrect;
    str += line;
    if (i !== data.length - 1) str += '\n';
  }
  return str;
}

if (Math.random() < incidence) {
  // parse the data file
  deserialize(dirName + fileName, function(err, data) {
    if (err) return console.log('Unknown error.', err);

    var answeredCorrectly = 0;
    var y0 = 2/(likelyRatio + 1);
    var a = 2*y0 - 2;
    var b = 2 - y0;
    do {
      // sort the data
      data.sort(function(a, b) {
        var aRatio = a.correct/(a.incorrect + 1)
        var bRatio = b.correct/(b.incorrect + 1)
        return aRatio - bRatio;
      });

      // select a word, weighted by correct/incorrect ratio
      var r = (-b + Math.sqrt(b*b + 2*a*Math.random()))/a;
      var idx = Math.floor(r * data.length);
      var word = data[idx];

      // quiz the user on that word
      var pos = answeredCorrectly + 1;
      var guess = readlineSync.question(
        '(' + pos + '/' + questionsPerIncident + ') ' +
        'What does "' + word.from + '" correspond to? '
      );
      if (guess === word.to) {
        answeredCorrectly += 1;
        data[idx].correct += 1;
      } else {
        data[idx].incorrect += 1;
        console.log(data[idx]);
      }

      // save the new data file every round
      var str = serialize(data);
      fs.writeFileSync(dirName + fileName, str)
    } while (answeredCorrectly < questionsPerIncident);
    console.log('--- --- ---');
  });
}

## words.txt
goodbye,tchau,0,0
yes,sim,0,0
your,seu,0,0
who,quem,0,0
good afternoon,boa tarde,1,0