World generation

This is a script that is supposed to create the floor around the player if there is not a block there already but it freezes up unity

 #pragma strict

 var X : int;
 var Y : int;
 var Z : int;
 
 var grassBlock : GameObject;
 var hill : GameObject;
 
 function Start()
 {
     while(1)
     {
         for(var i=(X-64) ; i<(X+64) ; i++)
         {
             for(var j=(Z-64) ; j<(Z+64) ; j++)
             {
                 if (!(Physics.Raycast (Vector3(i,0,j+2), Vector3.back, 2 )))
                 {
                     Instantiate (grassBlock, Vector3(i,0,j), Quaternion.identity);
                 }
             }
         }
         yield;
     }
 }
 
 function Update () 
 {
     X = transform.position.x;
     Z = transform.position.z;
 }