-- -- EXERCISE 5: using setup to create parsers, to test sentences
Try using the parser generator in lib grammar to test sentences that you
think your grammar and lexicon can handle.
If you have not compiled your grammar and lexicon since this editing
session started, go to your file containing them, mark the whole range,
from the 'vars' declaration to the end of the second assignment, to
blocks_lex. Then compile that range (CTRL-d). Test that you have
compiled both by printing out the grammar and the lexicon (ESC d on each
line):
blocks_gram ==>
blocks_lex ==>
Now make sure that the grammar library is loaded ( ESC d ):
uses grammar
A procedure you have not yet met is provided to create a collection of
parsers from your grammar and your lexicon. The procedure is called
setup. You can ask Pop11 what setup is
Use ESC-d:
setup =>
that prints out:
** <procedure setup>
NB in Pop11 procedures are objects just as lists, numbers, words,
strings, and arrays are (among other things).
We use setup to create parsers by applying the procedure to the grammar
and the lexicon (ESC-d):
setup(blocks_gram, blocks_lex);
That command does not print anything out but it creates a collection of
procedures for recognising items that the grammar deals with, one
procedure for each of the capitalised sentence components in the
grammar, and one for each type of word in the lexicon.
You can ask pop11 to print out some of the procedures
s =>
** <procedure s>
QUEST =>
** <procedure QUEST>
ONTO_PP =>
** <procedure ONTO_PP>
NOUN =>
** <procedure NOUN>
DET =>
** <procedure DET>
(You can think of these procedures as compiled versions of the grammar
rules. But they are procedures for recognition, whereas the grammar
rules can also be used for generation, as we saw previously.)
Try using the recognisers, and see if they do what they should do. The
lexical recognisers can only recognise words (represented in double
quotes in Pop11, if not in a list expression).
E.g. notice that DET returns a description of what it recognized:
DET("the") =>
** [DET the]
otherwise it returns one of Pop11's two booleans (true and false are
booleans):
DET("blue") =>
** <false>
Copy and edit the DET command and try it with other words from the
lexicon. Do the same with some of the other newly created procedures
for recognising lexical entries, e.g.
ADJ("red") =>
** [ADJ red]
ADJ("the") =>
** <false>
Now try some recognisers for complex constructs.
Reminder: these are the constructs (unless you changed the grammar):
s QUEST COM NP SNP AP PP ONTO_PP
Each now is the name of a procedure, e.g. (use ESC d):
QUEST, COM, PP =>
** <procedure QUEST> <procedure COM> <procedure PP>
So they can also be run. But because they come from the grammar, not the
lexicon, they must be applied to lists of words, not individual words.
E.g. run these (using ESC d on each), and try editing them to see what
results you get:
AP([big red]) ==>
** [AP [ADJ big] [AP [ADJ red]]]
The adjectival phrase is an adjectival phrase starting with and
adjective indicated by
[ADJ big]
and followed by an adjectival phrase indicated by
[AP [ADJ red]]
Compare these:
AP([the red]) ==>
** <false>
AP([big red box]) ==>
** <false>
But compare
NP([the big red box]) ==>
** [NP [DET the] [SNP [AP [ADJ big] [AP [ADJ red]]] [NOUN box]]]
This is noun phrase because it contains a determiner:
[DET the]
Followed by a simple noun phrase SNP, which is an AP followed by a NOUN
[SNP [AP [ADJ big] [AP [ADJ red]]] [NOUN box]]]
-- Using showtree -----------------------------------------------------
The library program showtree can be used to display the NP description
in a graphical format. (This will work in XVed, and also in Ved if you
are using an 'xterm' window, or using PuTTY in windows to access Poplog
remotely:
Compile the library (ESC d)
uses showtree
Apply the procedure to the full NP description (using ESC d):
showtree([NP [DET the] [SNP [AP [ADJ big] [AP [ADJ red]]] [NOUN box]]])
If it works on your terminal it will look something like this (only
prettier):
|NP|
-----------
|DET| |SNP|
| ---------
| | |
the |AP| |NOUN|
------- |
|ADJ| |AP| box
| |
| |
big |ADJ|
|
|
red
Now try testing sentences that you construct to see if the "top level"
parsing procedure "s" recognises them:
Examples:
s([which big box is above it]) ==>
** [s [QUEST [WH_SELECT which]
[SNP [AP [ADJ big]] [NOUN box]]
[VBE is]
[PP [PREP above] [NP [PN it]]]]]
Examine that closely to work out where all the descriptions come from.
Why doesn't this one work:
s([which large box is below it]) ==>
** <false>
Can you fix either the grammar or the lexicon, then recompile it, then
re-run the setup procedure so that that example is accepted?
The showtree library includes a pop11 macro "---" defined so that
showtree([ word word word ..... ] ) ==>
can be abbreviated like this and compiled as before.
--- word word word .....
e.g. try
--- is some box above it
** [s [QUEST [VBE is]
[NP [DET some] [SNP [NOUN box]]]
[PP [PREP above] [NP [PN it]]]]]
--- where are all the large boxes
** <false>
--- where is every large green box
** [s [QUEST [WH_LOC where]
[VBE is]
[NP [DET every] [SNP [AP [ADJ large] [AP [ADJ green]]] [NOUN box]]]]]
Try using some of the output of the generate(<grammar>, <lexicon>)
command, and see if the s procedure recognises everything generated,
and parses it correctly into sub-structures.
-- EXERCISE: Make a summary of what you have learnt from this file ----
-- TO BE ADDED --------------------------------------------------------
Further developments of these ideas
Designing and implementing a parser, instead of using lib grammar
Combining parsing with other components in a complete architecture, e.g.
for a chatbot or simple expert system, or travel adviser.
Combine the above ideas with an image analyser to generate descriptions
of what is in various images.
Combine the above ideas with a program for making pictures, and make it
draw a picture when given a sentence describing the desired contents.
What other applications can you think of?
Further reading
TEACH * ISASENT
TEACH * PARSESENT
TEACH * PARSING
--- $usepop/pop/teach/gram3
--- University of Birmingham 2011. All rights reserved. ------