In this assignment, you will implement a compiler phase that checks
whether a Joos 1W program satisfies certain basic validity requirements.
It is recommended that your design follow these four
stages: abstract syntax tree building, environment building, type name
resolution, and hierarchy checking.
A parse tree built using an unambiguous grammar typically contains
many redundant nodes. By recursively traversing the parse tree, it is
possible to build an abstract syntax tree with an analogous structure
but fewer nodes. An abstract syntax tree simplifies later phases of the
compiler by reducing the number of nodes and the number of different
kinds of nodes that each phase needs to handle. When a compiler is
implemented using a statically typed language, distinct types are
typically defined for each possible kind of tree nodes, so that later
compiler phases can use the type to document the tree nodes that they
The environment building stage creates environments (containing
classes, interfaces, fields, methods, local variables, and formal
parameters) for each scope. Given a name of one of these entities, the
environment should be able to locate the correct declaration of the entity.
After constructing all of the environments, the following requirements
of the Joos 1W language must be checked:
The type linking stage connects each use of a named type (class or
interface) to the declaration of the type. At this stage, only names
that can be syntactically (according to JLS 6.5.1) determined to be names of types need to be
linked. Some names are syntactically ambiguous, in the sense that type
checking must be done before it can be determined whether they are names
of types or of other entities (see JLS 6.5). These ambiguous names will
be linked in a later assignment.
When linking type names, the following requirements of the Joos 1W
language must be checked:
The fourth stage computes the inheritance relationships for classes,
interfaces, methods, and fields, and checks that they conform to
the various rules given in Chapters 8 and 9 of the Java Language Specification.
Specifically, this stage should check that:
A common error in this assignment is that the compiler works correctly only when the
source files are listed on the command line in a particular order, for example with
all superclasses before their subclasses. When designing your compiler, be sure to
consider that the source files could be listed in an arbitrary order. When testing your
compiler, make sure that it still works correctly when the source files are reordered.
You are not asked to submit a report for this assignment.
However, Assignment 4 will require a report covering
Assignments 2, 3, and 4, so it is recommended that you start writing
such a document. Your report will follow the guidelines.
As in Assignment 1,
you must hand in to Marmoset a .zip archive containing
your source code. It should include everything required to build and run your project.
In particular, in addition to your source code, it should contain a
file named Makefile. Marmoset will run make on this Makefile
to build your compiler. The Makefile must generate an executable
(binary or shell script) called joosc.
Unlike in Assignment 1, joosc in this and future assignments must be
able to accept multiple filenames as arguments. All of the files
listed on the joosc command line—and only those files—are considered
part of the program being compiled.
Unlike javac, your joosc compiler should not look for classes in
.class files on the CLASSPATH. Instead, it should read only those
Joos 1W source files listed on the command line. Thus, all classes,
including classes such as java.lang.Object, must be available in
source form and must be specified on the joosc command line. Unlike
javac, Joos does not care what directory a source file is in (i.e., it
does not require the directory structure of the source code to match
the package structure). However, the class declared in a file must
still have the same name as the filename.
For example, Java would require that the class java.lang.Object be
declared in the file Object.java in the directory java/lang,
whereas Joos only requires the file to be named Object.java but
otherwise allows it to be in any directory.
For the purposes of this course, a minimalist version of the Java
standard library is provided. This library can be found in the
linux.student.cs environment in the directory
/u/cs444/pub/stdlib/2.0. Marmoset will include all files in this
library on the joosc command line for every test, in addition to
other source file(s) specific to that test. The following versioning
scheme is used to make it possible to correct errors and/or to extend
the library for future assignments (although we aim to minimize the
number of changes that will be required). The 2 in the directory name
refers to Assignment 2, and the 0 is the first version of the library.
Any corrections to the Assignment 2 version of the library will appear
in the directories 2.1, 2.2, etc., and the version of the library
for Assignment 3 will appear in the directory 3.0.
As in Assignment 1, joosc should process the Joos 1W files given on
the command line, produce appropriate diagnostic messages on standard
error, and exit with one of the following Unix return codes:
The archive should include all your test cases and test code that you used to
test your program. Be sure to mention where these files are in your
report. Do not include Marmoset public tests.
The archive should include a file named a2.log showing the commit history
of your Git repository.
The archive should not include any extraneous non-source files.
It should not include any files that ought to be automatically
generated by building or running your compiler.
Your build process should not transmit data from/to the internet
in any way.
We reserve the right to deduct points if your submission does not
meet the requirements above.
The Marmoset tests for this assignment take several minutes to run.
Do not submit more than one submission at a time to Marmoset. If
Marmoset reports that your previous submission has not been tested
yet, do not submit another one. Denial-of-service attacks on Marmoset
will result in disciplinary action.