declarative style evaluation.js

declarative style evaluation.js

/*
http://twitter.com/#!/bga_/status/116861871423885312
*/


Object.prototype.thunk = function(name, calc) {
  Object.defineProperty(this,name,{get: function() { 
    var ret = calc();
    delete this[name] // memo result
    this[name] = ret;
    return ret;
  },configurable:true});
}

var solveQuadraticEquation = function(a, b, c) {
  with({})   {
    thunk('D', function(){ return b*b - 4*a*c });
    thunk('double_a', function(){return 2*a});
    thunk('sqrt_D', function(){return Math.sqrt(D)});
    thunk('x1', function(){ return (-b + sqrt_D) / double_a });
    thunk('x2', function(){ return (-b - sqrt_D) / double_a });
    if(D < 0)
      return [];
    else if(D == 0)
      return [x1];
    else	  
      return [x1, x2];
  }
}

console.log(solveQuadraticEquation(1, 0, -1));