3.4.4 Functional languages: Story Generation

Setup

Perform the weekly set up instructions for project 1, homework d.

What to hand in

Report (a) all the lisp functions you’ve written and (b) a file containing your deftests for all parts of the following and (c) ‘repl.txt’ coming from you saving the REPL showing these all running.

Exercise 1 : Write a Sci Story Generator (warning: slow)

Convert the file ‘1/d/scifi.txt’ into a grammar.

Run your terminal and lint tools over the result and show that your grammar is looking good. Fix any errors you find.

Exercise 2 : Generate 10 Sci Story (easy)

Write a deftest that generates 10 scifi stories.

Exercise 3: Caching Rewrites (hard)

The current grammar is stupid. Once it chooses a rewrite, then that rewrite is forgotten. So if it chooses a Boy’s name to be John then it instantly forgets it and the next reference to Boy might be John or Pima. For example, look at the mixed up sentences in the following:

(!generate2)

(
   (JOHN RUNS VERY VERY VERY QUICKLY SLOWLY WITH JOHN) ; ok
   (AJIT WALKS VERY VERY VERY VERY QUICKLY SLOWLY WITH JOHN) ; mixed up
   (JOHN WALKS VERY QUICKLY SLOWLY WITH AJIT) ; mixed up
   (JOHN WALKS QUICKLY SLOWLY WITH AJIT)      ; mixed up
   (JOHN RUNS QUICKLY SLOWLY WITH JOHN)       ; ok
   (AJIT WALKS QUICKLY SLOWLY WITH JOHN)      ; mixed up
   (AJIT RUNS QUICKLY SLOWLY WITH JOHN)       ; mixed up
)

This came from following grammar

(defparameter *grammar2*
	'((Sentence -> (Nounphrase Verbphrase))
	 (Nounphrase -> (Boy))
	 (Nounphrase -> (Girl))
	 (Boy -> john ajit)
	 (Girl -> pima barkha)
	 (Verbphrase -> (Verb Modlist Adverb with  Nounphrase))
	 (Verb -> runs  walks )
	 (Modlist ->  () (very Modlist))
	 (Adverb -> (quickly  slowly))))

Fix this. Rewrite ‘1/d/story.lisp’ such that for a set of pre-defined lefties (in our case Boy and Girl), once they are rewritten they always rewrite to the same thing. If you succeed then each generated sentence should never mix two boy or two girl names.

Test this caching version of ‘1/d/story.lisp’ on *grammar2*.

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