pcfg.wppl

var pcfgTransition = function(symbol) {
  var rules = {
    'start': {rhs: [['NP', 'V', 'NP'], ['NP', 'V']], probs: [0.4, 0.6]},
    'NP': {rhs: [['A', 'NP'], ['N']], probs: [0.4, 0.6]}
  };
  return rules[symbol].rhs[discrete(rules[symbol].probs)]
}

var preTerminal = function(symbol) {
  return symbol == 'N' || symbol == 'V' || symbol == 'A'
}

var terminal = function(symbol) {
  var rules = {
    'N': {words: ['John', 'soup'], probs: [0.6, 0.4]},
    'V': {words: ['loves', 'hates', 'runs'], probs: [0.3, 0.3, 0.4]},
    'A': {words: ['tall', 'salty'], probs: [0.6, 0.4]} }
  return rules[symbol].words[discrete(rules[symbol].probs)]
}

var pcfg = function(symbol) {
  preTerminal(symbol) ? [terminal(symbol)] : expand(pcfgTransition(symbol))
}

var expand = function(symbols) {
  if (symbols.length == 0) {
    return []
  } else {
    var f = pcfg(symbols[0])
    return f.concat(expand(symbols.slice(1)))
  }
}

var arrayEq = function(a, b) {
  return (a.length == 0) ? true : (a[0] == b[0] && arrayEq(a.slice(1), b.slice(1)))
}

Enumerate(function() {
  var y = pcfg('start')
  factor(arrayEq(y.slice(0, 2), ['tall', 'John']) ? 0 : -Infinity) //yield starts with "tall John"
  return y[2] ? y[2] : '' //distribution on next word?
}, 300)