CS 453 Programming Assignment #4 — Parsing

Due Wednesday, March 26th (by 11:59pm)
late policy

Preliminary Subversion Log
Due Friday, February 29th (by 6:00pm)
see below


For your last assignment, you created a description of the MiniJava tokens and had JLex generate a lexer for them. For this assignment you will write a description of MiniJava's grammar for JavaCUP and have JavaCUP build a parser for the language. Your goal is to describe a parser that constructs an abstract syntax tree (AST) for the given MiniJava program. You will do this by first specifying the grammar to JavaCUP and then associating actions to each of the grammar productions so as to construct an AST. The AST data structure will be provided.

Getting Started

As a starting point, download MJParseToASTStart.tar. MJParseToASTStart.tar provides you with the start of a MiniJava parser that is capable of parsing and generating the AST for a limited set of expressions. The directory structure is as follows:
                DepthFirstAdapter.java  // depth-first traversal over ast nodes
            ParserDot.java      // visitor that creates .dot file from AST
            minijava.cup        // grammar specification and actions
        ParseDriver.java        // driver that generates AST
Run ParseDriver on exp1.test and exp2.test. Visualize the generated .dot files by using the program dot, which is explained in the class setup notes.

The Assignment

Specify the full MiniJava grammar in minijava.cup. After the grammar has been specified and tested to make sure it accepts any syntactically legal MiniJava program and rejects illegal programs, add actions in minijava.cup that generate an ast. The ast.nodes package contains all of the ast node implementations along with appropriate constructors.

The .dot file generated by your parser will be compared to the one generated by the reference parser, MJParseToAST.jar. MJParseToAST.jar may be run in the usual way:

    % java -classpath java-cup-11a-runtime.jar -jar MJParseToAST.jar AllTypes.java

Step 1: Specify the MiniJava Grammar

The grammar for MiniJava is online here. It would be nice if you could just translate this into something that JavaCUP can understand and be done with it. Unfortunately, the grammar will need some modifications before it adequately describes the language. For expressions, use the following precedence, which is listed from lowest to highest with operators and tokens listed on the same line having equal precedence:
  1. Exp && Exp
  2. Exp < Exp
  3. Exp + Exp, Exp - Exp
  4. Exp * Exp
  5. ! Exp
  6. Exp [ Exp ], Exp . length, Exp . id ( ExpList )
  7. INTEGER_LITERAL, false, true, this, id, new id (), new int [ Exp ], ( Exp )
Of the above operators, only the not(!) operator has right-to-left associativity.

It is possible to specify subsets of the full MiniJava grammar so as to incrementally develop the grammar specification for JavaCUP. For example, the MJParseToASTStart project includes a minijava.cup file with a subset of possible expressions. The TestCases/ subdirectory includes two test cases for this restricted grammar: exp1.test and exp2.test.

Step 2: Generating the AST

After the parser being generated accepts syntactically legal MiniJava programs, it is time to add actions to the grammar for the construction of an abstract syntax tree. The AST is similar to the implicit parse tree, however it does not keep tokens around unless the tokens contain useful information (e.g. IDs and NUMBERS). See the minijava.cup file in MJParseToASTStart/src/mjparser/ to see some examples of how to generate an AST. We will also be discussing AST construction in class.


Some JavaCUP Pitfalls

Here are some issues that you might run into with JavaCUP:


Preliminary Subversion Log


  • Submit assignment using checkin utility
    ~cs453/bin/checkin PA4 MJParser-groupname.jar
  • Sanity Check (procedure TA will use to run your assignment):
      % java -classpath java-cup-11a-runtime.jar -jar MJParser-groupname.jar filename.java
      % mkdir MJParser-groupname/src/
      % cd MJLexer-groupname/src/
      % cp ../../MJParser-groupname.jar .
      % jar xf MJParser-groupname.jar
    Note that you need to have a copy of the java-cup-11a-runtime.jar file in the same directory as the MJParser-groupname.jar file. We will provide our own copy of the runtime jar file for testing. We will be running your parser on multiple test files. Also, the TA will be looking at the source files and possibly running JavaCUP on the minijava.cup file.
  • Late Policy:

    Late assignments will be accepted up to 24 hours past the due date for a deduction of 20% and will not accepted past this period.

    mstrout@cs.colostate.edu .... February 24, 2008
    Originally written by Brad Richards 2006, modified with permission by Michelle Strout 2007. Significantly rewritten and borrowed some from Sam Guyer's writeup of a similar assignment Michelle Strout 2008.