public STObject EvaluateAssignSend(STObject receiver, Node assignSend, Context context)
{
STObject other = EvaluateExpression(assignSend.GetChildAt(1), context).Dereference();
var variable = receiver as STVariable;
if (variable == null)
throw new Exception ("Error: can only assign to a valid variable lvalue");
variable.Set(other);
return other;
}