new function: list-kets

So, I guess this thing could be called the brother of rel-kets[op]. The idea is simply, return a superposition of all known kets that match the pattern.

eg:
list-kets |movie: *> returns the list of all movies (in the current context)
list-kets |person: *> returns the list of all people
list-kets |animal: *> returns the list of all animals
list-kets |*> returns all kets with learn rules.

Here is the python (in the new_context class):

# e is a ket.
  def list_kets(self,e):
    label = e.the_label()
    if len(label) == 0:
      return ket("",0)
    if label[-1] != "*":
      return e
    label = label.rstrip("*").rstrip(": ")
    result = superposition()
    for trial_label in self.ket_rules_dict:
      if trial_label.startswith(label):
        result.data.append(ket(trial_label))  
    return result

I hope that is simple and obvious enough. Should be useful in a bunch of places.

As usual, more to come!

Update: here is a quick example. What is the list of animals with 4 legs?
such-that[has-4-legs] list-kets |animal: *>

Update: For now I have deprecated list-kets. I have replaced it with starts-with.
eg, list of animals with 2 legs?
such-that[has-2-legs] starts-with |animal: >

eg, list all kets that have Fred as a first name?
starts-with |Fred >

eg, list all kets:
starts-with |>

Here is the new python:

# e is a ket.
  def starts_with(self,e):
    label = e.the_label()
    result = superposition()
    for trial_label in self.ket_rules_dict:
      if trial_label.startswith(label):
        result.data.append(ket(trial_label))  
    return result

That's it for now. Hrmm... I wonder if I broke any code with this change?