Experimenting with Antlr grammar syntax

English.g4

grammar English;

paragraph: sentence+ EOF;

sentence: prepositionalPhrase* subject activeVerb directObject indirectObject? prepositionalPhrase* '.'
        | prepositionalPhrase* subject? toBeVerb  (directObject | adjective)? prepositionalPhrase* '.'
        | toBeVerb subject (directObject | adjective)? prepositionalPhrase* '?';

subject: nounPhrase;
directObject: nounPhrase;
indirectObject: nounPhrase;

nounPhrase: article? nounModifier* noun;
nounModifier: adjective | possesive;

prepositionalPhrase: preposition nounPhrase;

possesive: noun '\'s';

noun: 'dog' | 'cat' | 'Alice' | 'Bob' | 'things';
activeVerb: 'tells' | 'sees' | 'hears';
toBeVerb: 'is';
article: 'a' | 'the';
adjective: 'bored' | 'shy' | 'sleepy';
preposition: 'about' | 'from' | 'behind';

WS: [ \t\f\n\r] -> skip;

//Alice tells sleepy Bob about the bored cat.
//Bob sees Alice's things behind the dog.
//Bob's cat is shy.
//behind the cat is a bored dog.
//a bored dog is behind the cat.
//Bob tells Alice things about the dog.
//Bob is sleepy from the things behind the dog.
//is Bob shy about sleepy Alice?

// abouttheBobboreddog'ssleepysleepysleepycattellsdogaAlicefromshycat.