In this part of the project you write a lexer for µOCCAM, using flex, and a parser, using bison. The grammar is described in Chapter 1 of the µOCCAM manual. Your program should read text from the standard input and determine whether or not it is valid µOCCAM code. This recogniser forms the front end for the compiler you will build in phase 2.
At this stage your solution only needs to deal with syntactic issues. For
example, you do not have to make certain whether a procedure call has the
right number of arguments, or if a channel is used where there should be an
integer. This sort of check will form part of the second stage of the
project. If you are unsure whether or not your program should include a
particular check, just ask.
In the opening lecture you saw a tiny example of a recogniser for µOCCAM -- one that only accepted very few programs. This is the code you should start with. It works, but only just, and offers ample opportunity for improvement. Start as follows.
occamprogram's answer: 0 for success or 1 for failure. This variable
$?is the return code.
||specifies the lexer;|
||specifies the parser;|
|describes how |
The best way to find out how good is your recogniser is to test it on valid
and invalid µOCCAM programs. You can do this using the
ipp test program, as follows.
Then run ipp -1 (or just ipp1) to get a summary of your
recogniser's performance on the sample µOCCAM code. A detailed log file is
ipplog. For more information, including a host of
configuration options, see the full program
There is a catalogue of examples provided by students. During this stage of the practical you must contribute at least one test program to this.
To submit your code, execute the ipp1submit command. This will
hand in all text files in your
~/ipp1/ directory. You can submit
as many times as you like -- only the last version will be kept, with a record
of the time of submission. You must submit your work by 12 noon on
Tuesday 14 November.
Here are the necessary steps, in detail.
cp -r ~/ipp1 ~/ipp1backup
~/ipp1/only contains the minimum text files needed to recreate your
occamprogram. For most of you, this means just
Makefile. One way to tidy things up is with cd ~/ipp1; make clean
The submission program will give errors if there is no
directory, or if it is readable by anyone other than yourself. If it fails
for any other reason, please email me
with a copy of the error message.
Finally, remember that there are also marks for contributing at least one test program to the catalogue.
Once submitted, your source code will be placed in a directory of its own.
make command will be executed in that directory to build your
compiler. The resulting executable
occam will be run once with
each of a batch of test µOCCAM files as input. Your program's return code in
each case (0 or 1) will be recorded and compared with the correct answer.
Credit for the practical is assessed over a range of areas, including the following.
The last item is the most substantial.
Separately from the assessment, your submitted files may undergo a certain amount of analysis to discount plagiarism.