Directional Prepositions
Let’s implement the verb “go” in hello_world.py to allow for moving around the file system in a simple way.
The phrase:
go to a folder
… yields 4 parses, one of which is:
***** Parse #3:
Sentence Force: comm
[ "go to a folder"
TOP: h0
INDEX: e2 [ e SF: comm TENSE: pres MOOD: indicative PROG: - PERF: - ]
RELS: < [ pronoun_q<0:14> LBL: h4 ARG0: x3 [ x PERS: 2 PT: zero ] RSTR: h5 BODY: h6 ]
[ pron<0:14> LBL: h7 ARG0: x3 ]
[ _go_v_1<0:2> LBL: h1 ARG0: e2 ARG1: x3 ]
[ _to_p_dir<3:5> LBL: h1 ARG0: e8 [ e SF: prop TENSE: untensed MOOD: indicative PROG: - PERF: - ] ARG1: e2 ARG2: x9 [ x PERS: 3 NUM: sg IND: + ] ]
[ _a_q<6:7> LBL: h10 ARG0: x9 RSTR: h11 BODY: h12 ]
[ _folder_n_of<8:14> LBL: h13 ARG0: x9 ARG1: i14 ] >
HCONS: < h0 qeq h1 h5 qeq h7 h11 qeq h13 > ]
-- CHOSEN Parse #0, CHOSEN Tree #0:
┌────── _folder_n_of(x9,i14)
_a_q(x9,RSTR,BODY) ┌────── pron(x3)
└─ pronoun_q(x3,RSTR,BODY) ┌── _to_p_dir(e8,e2,x9)
└─ and(0,1)
└ _go_v_1(e2,x3)
It introduces two additional predications we’ll need to implement to make this work: _to_p_dir and _go_v_1.
_to_p_dir
_to_p_dir is a directional preposition. Directional prepositions usually end with _dir and have the signature (e, e_verb, x_location). x_location indicates the location the preposition is specifying, and e_verb indicates the event (often a verb) that this preposition should be attached to. They specify a particular direction in which to do something. The fact that the predication takes an event as its second argument is a hint that the predication itself doesn’t do anything except attach its information to the specified event so that something else can use it. Taking an event as an argument besides ARG0 usually indicates the predication is modifying the event. So, it can be implemented like this:
@Predication(vocabulary, names=["_to_p_dir"])
def to_p_dir(state, e_introduced, e_target_binding, x_location_binding):
preposition_info = {
"EndLocation": x_location_binding
}
yield state.add_to_e(e_target_binding.variable.name,
"DirectionalPreposition",
{"Value": preposition_info,
"Originator": execution_context().current_predication_index()})
This code just adds the location x_location to the e_target event under the key DirectionalPreposition. This allows the event that introduces it to consume it, as discussed in a Event Predications topic. The Predication class will ensure that the user will get a “don’t understand” error if the predication that introduced the event doesn’t know how to handle it, as discussed in that same topic.
_go_v_1
Next, we need to implement _go_v_1, indicating that it does know how to handle that information, like this:
@Predication(vocabulary,
names=["_go_v_1"],
handles=[("DirectionalPreposition", EventOption.required)])
def go_v_1_comm(state, e_introduced_binding, x_actor_binding):
if x_actor_binding.value is None or len(x_actor_binding.value) > 1 or x_actor_binding.value[0].name != "Computer":
report_error(["dontKnowActor", x_actor_binding.variable.name])
return
x_location_binding = e_introduced_binding.value["DirectionalPreposition"]["Value"]["EndLocation"]
def bound_location(location_item):
# Only allow moving to folders
if isinstance(location_item, Folder):
return True
else:
if hasattr(x_location_binding.value, "exists") and location_item.exists():
report_error(["cantDo", "change directory to", x_location_binding.variable.name])
else:
report_error(["notFound", x_location_binding.variable.name])
def unbound_location(location_item):
# Location is unbound, ask them to be more specific
report_error(["beMoreSpecific"])
# go_v_1 effectively has two arguments since it has x_actor by default and requires x_location from a preposition
for new_state in individual_style_predication_1(state,
x_location_binding,
bound_location,
unbound_location,
["cantDo", "go", x_location_binding.variable.name]):
yield new_state.apply_operations([ChangeDirectoryOperation(new_state.get_binding(x_location_binding.variable.name))])
The handles=[... EventOption.required ...] clause on Predication tells the system that this predication requires a directional predication and the system ensures that it won’t get called if it isn’t there. That is why the code can just assume it is there and access the EndLocation key without checking for its existence first in this line:
x_location_binding = e_introduced_binding.value["DirectionalPreposition"]["Value"]["EndLocation"]
The function starts with code for making sure the user specified an actor and didn’t say “he goes to a folder” or “mary and bill go to a folder”, we only support “you”.
Next, the bound_location() function has code to check if the object passed in actually exists so that it can return a more specialized error if the user asks to go somewhere that doesn’t exist. Otherwise, they’d get the error “I can’t go to X” if the folder doesn’t exist, which is a little obtuse.
And finally, we handle this as an action verb, just like we handled “delete” in the Action Verbs topic, with one difference: _go_v_1 only has one non-event argument which represents “who is doing the going” (i.e. the actor). But, because we say we handle DirectionalPreposition in the introduced event and mark it as EventOption.required, it will always be there if this function is called. Thus, the location is effectively acting like a second x argument. So, in effect, we converted the predication to look just like _delete_v_1.
So, for the same reasons we had there, we can just handle the actor argument directly, and only have to call individual_style_predication_1(), treating it like a one x variable predication. We are doing individual_style instead of combinatorial_style for the same reasons _delete_v_1 did: we don’t have a way to implement the semantic of “go to folder1 and folder2” (let alone “together” or “separately”). So, go_v_1_comm will only handle going to a single location.
ChangeDirectoryOperation
Changing the directory, just like deleting a file in the Action Verb topic, is modifying system state. So, we need to create an Operation to do the work:
class ChangeDirectoryOperation(object):
def __init__(self, folder_binding):
self.folder_binding = folder_binding
def apply_to(self, state):
state.file_system.change_directory(self.folder_binding)
The operation uses a built-in method of the FileSystem object to change the directory.
Putting those three objects into hello_world.py, with the following reset() function:
def Example23_reset():
return FileSystemState(FileSystemMock([(True, "/documents/file1.txt", {"size": 1000}),
(False, "/Desktop", {"size": 10000000}),
(True, "/Desktop/the yearly budget.txt", {"size": 10000000}),
(True, "/Desktop/blue", {"size": 1000})],
"/Desktop"))
… allows us to do this:
python hello_world.py
? where am i
(Folder(name=/Desktop, size=10000000),)
(there are more)
? go to a folder
Done!
(there are more)
? where am i
(Folder(name=/documents, size=0),)
(there are more)
The system says “(there are more)” in response to “where am i” because the user is in both “/Desktop” and “/”. The reasons are described in the Combinations and Proper Responses topic. The same is true for “go to a folder” … there are several folders.
Comprehensive source for the completed tutorial is available here.
Last update: 2023-05-16 by EricZinda [edit]