1.7 Practical Session

We will start out with a couple of simple keyboard exercises so make sure that you understand how the Prolog programs that we saw in this section work.

Start Prolog and consult recognise1.pl, recognise2.pl, and haha1.pl. Using both test1 (which calls recognise1) and test2 (which calls recognise2) see whether various strings are accepted e.g
test1([h,a,!]). test2([h,a,!]). test1([h,a,h,a,h,a,!]).
Make sure you understand why these strings are accepted. That is, use trace to step through the execution so that you understand exactly what is going on.
Restart Prolog and consult recognize1.pl, recognize1.pl, and haha5.pl. The difference between haha1 and haha5 is that haha5 is not deterministic. Try giving the following queries.
test1([h,a,!]). test2([h,a,!]). test1([h,a,h,a,h,a,!]).
Make sure you understand why these strings are accepted. That is, use trace to step through the execution so that you understand exactly what is going on.
Now restart Prolog and consult recognize1.pl, recognize2.pl, and haha2.pl. The big difference between haha1 and haha2 is that haha2 contains a jump arc #. Now, recognizer1 does not handle jump arcs so it should not be able to handle haha2 correctly. Try out the following experiments, and make sure you understand why recognize1 gives the responses it gives:
| ?- test1([h,a,!]). yes | ?- test1([h,a,h,a,!]). no | ?- test1([h,a,h,a,h,a,!]). no
Now try these examples with test2. Again, carry out traces. Try using generate1 to generate using haha2. Now try using generate2 with haha2. Why does generate1 give a wrong response?
Finally, make sure that you understand how the generate predicates are defined. In particular, make sure you understand what the `fail' in the generate3 predicates does.

Now, you are able to write your own automata. You can then use the recognize and generate predicates to test them. So, here is a task which is a bit more interesting: Write an FSA (First, as a graph and, then, in Prolog notation!) that recognizes English noun phrases constructed from the following words: a, the, witch, wizard, Harry, Ron, Hermione, broomstick, brave, fast, with, rat. E.g.

the brave wizard
the fast broomstick
the wizard with the rat
Ron
...