FRP.js

require('allthemagicalstuff');

//event object constructor;
function event (target, eventName) {
  return {
    target: target
  , eventName: eventName
  };
};

/*
 * SIGNALS
 */
var MouseE , mouseS;
MouseE.clicks = event(document, 'click');
MouseS.position = function (e) { 
  return sigReturn({x:e.pageX, y:pageY});
};

//compound signal
function sampleOn (ev, signal) {
  var samples = [];
  var signal = extend(function () {
    return sigReturn(samples);
  }, EventEmitter);
  //under the hood we use eventemitter
  ev.target.addEventListener(ev.eventName, function (e) {
    samples.push(signal(e));
    signal.fire('change');
  });
  return signal;
}

//signal monad
//make user inaccessible to the raw signal out side
function sigReturn (signal) {
  return {
    '>>=': function (f) { return f(signal) }
  }
}


var clickLocations = sampleOn(MouseE.clicks, MouseS.position); //is a compound signal


//capture the scene
function scene (locs) {
  return sigReturn(map(drawPoint, locs));
};

function drawPoint (pt) {
  pt['>>='](function (p) {
    canvas.point(p.x, p.y); //side effect
  });
  retrun pt;
};

function lift (f, sig) {
  sig.addEventListener('change', function () {
    sig()['>>='](f);
  });
}

clickLocations()['>>='](scene);
lift(scene, clickLocations);



/*
 * Helpers
 */
function extend (dst, src) {
  var k;
  for (k in src)
    if (src.hasOwnProperty(k))
      dst[k] = src[k];
  return dst;
}

var EventEmitter = {
  listeners: []
, addEventListener: function (ev, f) {
    this.listeners.push({ev:ev, f:f});
  };
, fire: function (ev, o) {
    this.listeners
    .filter(function (x) {return x.ev === ev})
    .forEach(function (l) {
      l.f(o);
    });
  }
};

signal (behaviourとも言う)は関数で表現.
eventはDOMのターゲットとイベント名のペア.
lift(f,s)はsignal sが変化する度に関数fをsに適用するようにする.
f(s)はその時点でのシグナルがfに渡る.

signalはモナドかなにかでピュアな関数から隔離して閉じ込めたい