Grammar development

For this assignment, you will be editing a file named
'assignment4.py', which you can download from:

    http://nltk.org/temp/assignment4.py

Please rename this file to
'assignment4-<your last name>.py' before submitting it.


1. Chose a linguistic phenomenon of interest that you would like to
   model using a grammar.  Here are some ideas, or use your own:

     - Noun modifiers
       ("slow cat", "very slow cat")
     - Comparative expressions
       ("bigger than a breadbox", "less heavy than ...")
     - Sentential complements
       ("I think that you know that ...")
     - Quantifiers
       ("For every boy, some girl ...")

2. Choose 4-5 example sentences, and add them to the 'sent_corpus'
   variable.  This variable contains a list of sentences, one per
   line.

3. Add grammar and lexical rules to the 'grammar' variable to cover
   your example sentences.  

4. Run the program, and check the parse trees you get.  Were there any
   extra parse trees you weren't expecting?  Were there any sentences
   that failed to parse?

5. Refine your grammar until it covers your example sentences.  If
   possible, your grammar should not produce extra unintended parse
   trees.  (But for some linguistic phenomena, this might not be
   possible!)

6. Once you're happy with the output parse trees, copy them to the
   'tree_corpus' variable.  Do NOT copy the sentence strings -- just
   the tree expressions.  (If your grammar generates extra unintended
   parse trees, don't include them.)  You can then delete these
   sentences from 'sent_corpus'.  Run the program again, and it will
   automatically check to make sure that the intended parse trees are
   getting generated.  This way you won't have to keep checking them
   by hand if you choose to do the optional step (7).

7. Optional: return to step 2 (as many times as you like).

8. Use the 'comments' variable to write a short comment about grammar
   development -- was it easier or harder than you thought?  How hard
   do you think it would be to merge the grammar that you developed
   with some of your classmates' grammars, that were designed to
   handle other linguistic phenomena?  What problems might come up
   when merging grammars?