CS 444/644 - Compiler Construction (Winter 2021) - Assignment 3

For the third assignment, you will implement disambiguation of names and type checking.

As in Assignment 2, you must hand in to Marmoset a .zip archive containing your source code. The .zip file must contain a file called Makefile. Marmoset will run make on this Makefile to compile your compiler. The Makefile must generate an executable (binary or shell script) called joosc. The joosc executable must 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 and unlike the dOvs version of Joos, your joosc compiler should not look for classes in .class files on the CLASSPATH; it should read only the Joos 1W source files listed on the command line. This means that 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/3.0. 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 3 in the directory name refers to Assignment 3, and the 0 is the first version of the library. Any corrections to the Assignment 3 version of the library will appear in the directories 3.1, 3.2, etc., and the version of the library for Assignment 4 will appear in the directory 4.0.

Version 3.0 of the standard library is identical to version 2.0.

As in previous assignments, 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 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.

You are not required to submit a design document for this assignment. However, Assignment 4 will require a design document covering your design decisions for Assignments 2, 3, and 4, so it is recommended that you start writing such a document. As for Assignment 1, the document should be organized to enable someone unfamiliar with your code to understand the structure of your compiler. In the document, discuss challenges that you encountered and how you tried to overcome them in your design and implementation. Also explain the testing that you did before submitting to Marmoset.

Disambiguation and Linking of Names

The disambiguation stage determines the meaning of each remaining use of a name, and links the use to the declaration of the entity (field, method, local variable, formal parameter, or type) that the name refers to. Disambiguation of syntactically ambiguous names is specified in Section 6.5.2 of the Java Language Specification and was discussed in class.

Note that Joos 1W supports a simplified version of method overloading compared to the full Java overloading rules detailed in Section 15.12.2 of the Java Language Specification. Although Joos 1W does allow method overloading (i.e. multiple methods with the same name, but different parameter types), the declared types of the parameters must exactly match the static types of the argument expressions in order for the method to be called. For example, a call such as bar('x') will not invoke a method with signature bar(int), as it would in Java, but the call bar((int)'x') would.

If a prefix of a name refers to a variable or field, then the remaining part of the name refers to non-static field(s) or a method of the object referred to by that variable or field. At this stage, non-static fields and methods are not resolved; this is deferred until the type checking stage, when the static type of the base variable or field is known.

During and/or after disambiguation of names, the following restrictions of the Joos 1W language must be checked:

Type Checking

The type checking stage determines the types of all expressions and subexpressions, checks that they conform to the Joos 1W typing rules, and links all remaining names (i.e. non-static field accesses and method calls) to the declarations that they refer to.

It is possible for a class to contain multiple methods with the same signature, all abstract, and all inherited from one of its superclasses. In this case, the method call may be linked to any one of these methods, since they are guaranteed to have the same return type.

During and/or after type checking, the following restrictions of the Joos 1W language must be checked: