520-compiler

A "miniJava" compiler, as created for COMP 520, aimed at the mJAM VM.

Note that partly owing to class requirements, time requirements, and mJAM restrictions, my code is not as perfect as I want it to be. Please forgive me.

Features supported

The compiler parses for correct syntax, builds an AST, performs contextual analysis (identification and type checking), and code generation. miniJava supports variables, integer and boolean operations, basic control logic, arrays, some level of OOP, and an incomplete amount of support for overloading.

Extensions (PA5)

• Modulus (%) support (see ModTest.java).
• Static initialization block support (see StaticInitBlockTest.java).
• Constructor support, with support for parameters (see ConstructorTest.java). No support for overloading.
• System.exit support (see SystemExitTest.java). Doesn't do anything with the parameter, just halts.
• Basic for loop support, with optional components (see ForTest.java).
• Field initialization, including non-static initialization (see FieldInitializationTest.java).
• Overloading of methods (see OverloadingTest.java). Right now it's pretty broken but it works in some select cases.

Usage

The compiler should be used through the command line, through arguments:

• The first argument is the file to be compiled.
• A second optional argument that can be supplied is a "special mode" that can stop the compiler early, so no errors are generated. The following are supported:
  • --ast-only: scans, parses, builds an AST, and prints the AST.
  • --contextual-analysis-only, scans, parses, builds an AST, performs contextual analysis (just identification/type checking).
  • --asm-too, scans, parses, builds an AST, performs contextual analysis, code generation, and also outputs a dissambled .asm file.
  • --run, scans, parses, builds an AST, performs contextual analysis, code generation, outputs a dissambled .asm file, runs file that was generated.

Grammar

• Program ::= Class* end
• Class ::= class Id { ClassMember* }
• ClassMember ::= FieldDeclaration (FieldTail|Method) | static StaticBlock | Constructor
• FieldDeclaration ::= (public|private)? static? (Type|void) Id
• FieldTail ::= (= Expression)?;
• Method ::= **(**ParamList* **){**Statement* }
• StaticBlock ::= { Statement* }
• Constructor ::= (public|private)? Id **(**ParamList* **){**Statement* }
• Type ::= boolean|((int|Id)([])?)
• ParamList ::= Type Id(, Type Id)*
• ArgList ::= Expression(, Expression)*
• Reference ::= (Id|this)(**.*Id)
• Statement ::= PureStatement**;** | { Statement* } | if(Expression) Statement (else Statement)? | while(Expression) Statement | for(PureStatement?; Expression?; PureStatement?) Statement
• PureStatement ::= return (Expression)?** | Type Id = Expression | Reference([Expression])? = Expression | Reference**(ArgList?)**
• Expression ::= OrExpression
• OrExpression ::= AndExpression (|| AndExpression)*
• AndExpression ::= EqualityExpression (&& EqualityExpression)*
• EqualityExpression ::= RelationalExpression ((==|!=) RelationalExpression)*
• RelationalExpression ::= AdditiveExpression ((<=|<|>|>=) AdditiveExpression)?
• AdditiveExpression ::= MultiplicativeExpression ((+|-) MultiplicativeExpression)*
• Multiplicative ::= UnaryExpression ((*|/|%) UnaryExpression)*
• UnaryExpression ::= ((-|!) UnaryExpression) | PureExpression
• PureExpression ::= (Expression) | Literal | new (int[Expression]|Id((ArgList?)|[Expression])) | Reference([Expression]|(ArgList?))?
• Id ::= [\w**$_**][\w\d]+
• Literal ::= \d(\d)+ | true | false | null

The grammar above uses EBNF with some POSIX conventions sprinkled in to make my life easier. Whitespace is generally insignificant, but there must be spaces between identifiers/literals and so on.

License

As you can see in the license file, this project is under the "Unlicense" which effectively releases it into the public domain. Basically, do what you want with my semi-functional code. However, I don't recommend using the code for reference for COMP 520; Professor Prins explicitly doesn't allow this, and the particular subset to implement will change year-to-year. And of course, you will find it more rewarding to create something by yourself from scratch.

I have taken some test files from others, including Ben Dod, Changon Kim, and Professor Jan Prins, which are unlicensed. I have noted as such where I have used them. The classes in the AbstractSyntaxTrees package were made by Professor Prins with some changes as describes below, and the classes in the mJAM package were made by him too (with unlisted modifications by me).

Changes made to classes in the AbstractSyntaxTrees package

• Added support for null (adding NullLiteral.java, and updating Visitor.java and ASTDisplay.java to support it).
• Added decl field to Identifier.java and Reference.java for contextual analysis, along with an alternative constructor to initialize Identifier.java. Added inClass field to MethodDecl.java and FieldDecl.java for contextual analysis.
• Added alternative constructor to FieldDeclList.java, MethodDeclList.java, and ParameterDeclList.java to accept one declaration for convenience, which is to be appended to the list.
• Added abstract equals and toPrettyString methods in TypeDenoter.java, accompanied with implementation in BaseType.java, ClassType.java, and ArrayType.java. Added equals to Identifier.java and Declaration.java.
• Added isInitialized field to VarDecl.java, defaulted to false, which is used for contextual analysis (a [local] variable cannot be used if it has not been initialized).
• Added main field (of type MethodDecl) to Package.java to help with code generation.
• Added RuntimeDescriptor.java, with corresponding MethodDescriptor.java, ClassDescriptor.java, VarDescriptor.java. Added runtimeDescriptor field to Declaration.java.
• Added StaticBlockDecl.java, accompanied with a staticBlockDecl field in ClassDecl.java.
• Added ConstructorDecl.java, accompanied with a constructorDecl field in ClassDecl.java. Modified NewObjectExpr.java to include an argList field.
• Added ForStmt.java, accompanied with an update to Visitor.java (and ASTDisplay.java)
• Added initExpression field to FieldDecl.java and toInitialize field to ClassDecl.java.
• Syntactical/code style changes/cleanup.

Testing

This project uses JUnit for testing. I have my own tests, as well as added from others. There are also "checkpoint" tests, which are given by Professor Prins, which use Checkpoint1.java, Checkpoint2.java, etc., as controllers, and the files in pa1_tests, pa2_tests, etc., as the sample test files.

Credits

• Eric Schneider
• Jan Prins (AbstractSyntaxTrees package, mJAM package, checkpoint tests, Test7.mjava, Test34.mjava, Test35.mjava, Test62.mjava)
• Max Beckman-Harned (checkpoint tests)
• Ben Dod (Test2.mjava, Test3.mjava)
• Changon Kim (Test9.mjava)