Last updated: Sun 7 Apr 2024 18:29:52 AEST.
PL0 Compiler Java Source Code (Java-CUP generated
version)
The main changes from the assignment 1 compiler are in the package parse which makes use of the
parser and lexical analyser generators.
The Java files that make up the compiler are listed below, along with a brief description of their
purpose. The source code for the compiler is divided into the following packages:
pl0 contains the Java files for the main program for the compiler
parse contains the Java files to handle scanning and parsing as well as defining the lexical
tokens (major changes from assignment 1 approach)
tree contains the abstract syntax tree, the static semantic checker and the code generator
syms contains the symbol table, its entries, and type descriptors
machine contains the Java files for the stack machine interpreter, instruction set operation
codes, and instructions.
source contains the Java files for processing the source input and handling error messages
Package pl0
You shouldn't need to look in here too much. The main program defines some command line
arguments that may be useful.
PL0_LALR.java (class) The main program for the compiler ("LALR" stands for the LALR parser
generator Java-CUP).
Package machine
You may want to look inside the stack machine at some stage to work out exactly what an instruction
does.
Instruction.java (class) Defines the different formats of instruction.
Operation.java (enumeration) Define the operation codes for the stack machine.
StackMachine.java (class) Implements an interpreter for the Stack Machine.
Package parse
You'll need to understand how the Parser works and what the lexical Tokens are, but you shouldn't
need to look at the Scanner. The whole approach to parsing is completely different to assignment 1.
PL0.cup (Java-CUP specification for PL0 parser) The parser recognises the input program and
creates and abstract syntax tree.
PL0.flex (JFlex specification for PL0 lexical analyser) The lexical analyser recognises the input
character stream and splits it up into a stream of lexical tokens.
CUPScanner.java (class) A tiny bit of plumbing between the lexical analyser (Lexer) and the
parser generated by CUP.
CUPParser.java (class) The parser (written in Java) generated from PL0.cup. You should not edit
this directly; edit PL0.cup and re-generate this. If you get Java errors in this file, they usually
correspond to something invalid in one of the semantic actions within your PL0.cup
specification; try to determine what is wrong in the Java but then fix the corresponding action in
PL0.cup.
CUPToken.java (interface) A Java interface defining all the lexical tokens. This file is generated
by Java-CUP from the terminal symbol specifications within PL0.cup. If it is incorrect do not
modify this file, but modify PL0.cup and re-generate this file using Java-CUP.
Lexer.java (class) The lexical analyser or scanner (written in Java) generated from PL0.flex.
Package tree
You'll need to know the structure of the Abstract Syntax Tree and the definitions of the Operators.
Then you'll need to understand how the StaticChecker and CodeGenerator work. These both
implement the Visitor interfaces to traverse the abstract syntax tree.
Code.java (class) Data structure for a sequence of instructions used in the code generation.
CodeGenerator.java (class, implements TreeTransform, ExpTransform, and StatementTransform)
Implements the code generation for the compiler via a tree traversal.
ConstExp.java (class) Symbolic constant expressions are evaluated at compile time. This class
provides tree nodes to represent constants and evaluate them.
DeclNode.java (class) This class provides the abstract syntax tree nodes representing
declarations lists and procedure declarations.
DeclVisitor.java (interface) Visitor interface for declarations and procedures (including main
program).
ExpNode.java (class) Defines the nodes in the abstract syntax tree for expressions as well as
methods for allowing tree traversals using the visitor pattern.
ExpTransform.java (interface) Visitor interface for expressions returning a transformed
expression.
Operator.java (enumeration) Enumeration for the binary and unary operators for the abstract
syntax tree.
Procedures.java (class) Provides data structure to keep track of the start and finish addresses of
procedures. Also used to provide a run-time stack trace (on a run-time error).
StatementNode.java (class) Defines the nodes in the abstract syntax tree for statements as well
as methods for allowing tree traversals using the visitor pattern.
StatementTransform.java (interface) Visitor interface for statement transformation (used in
code generation).
StatementVisitor.java (interface) Visitor interface for statements (used by static checker).
StaticChecker.java (class, implements TreeVisitor, ExpTransform, and StatementVisitor)
Implements the static (type) checking for the compiler via a tree traversal.
Package syms
This package defines the symbol table and its entries as well as type descriptors.
Predefined.java (class) Handles all the predefined constants, types and operators.
Scope.java (class) Provides a single scope within the symbol table.
SymEntry.java (class) Defines the symbol table entries for CONST, TYPE, VAR and PROCEDURE
identifiers, and operators.
SymbolTable.java (class) The main symbol table that puts together symbol tables for each
Scope (procedure, main program or predefined scope) that contain entries (SymEntry) for each
identifier. Handles constant, variable, type, procedure identifiers, as well as the type structures.
SymbolTableTest.java (JUnit test class) JUnit test for the symbol table.
Type.java (class) Defines the symbol table structures that represent types, including basic types
like int and boolean, as well as subrange types.
TypeTest.java (JUnit test class) JUnit test for types.
Package source
This is low level boring stuff. You shouldn't have to look in here unless you just want to find out what
it does.
CompileError.java (class) Stores a single error message.
ErrorHandler.java (class, implements Errors) Handles the saving and reporting of error
messages.
Errors.java (interface) Errors interface defines error methods.
LineLocations.java (class) Used for finding the source line in the input file when reporting
errors.
Severity.java (enumeration) Enumeration containing the error message severities.
Source.java (class) Handles reading the source input, keeping track of the location within the
source input and output of error messages and a listing of the input.
Other files
Test programs
test-pgm/ A directory containing a set of test PL0 programs (each with suffix ".pl0").
Java-CUP and JFlex archives
java-cup-11b.jar The Java archive containing the parser generator Java-CUP.
jflex-full-1.9.1.jar The Java archive containing the lexical analyser generator JFlex.
For Eclipse
build-cup.xml An ant script for running the parser generator Java-CUP on PL0.cup to generate
CUPParser.java and CUPTokens.java. Can be used within Eclipse.
build-jflex.xml An ant script for running the lexical analyser generator JFlex on PL0.flex to
generate Lexer.java. Can be used within Eclipse.