Gold Parser

transcript

6/24/2004 SEKE 2004 1

GOLD: A Grammar Oriented GOLD: A Grammar Oriented Parsing SystemParsing System

Devin Cook and Du ZhangDevin Cook and Du ZhangDepartment of Computer ScienceDepartment of Computer Science

California State UniversityCalifornia State UniversitySacramento, CA 95819-6021Sacramento, CA 95819-6021

Introduction

• What is a Parser?– Software which breaks a source program into

its various grammatical units w.r.t. a formal grammar

– Used to convert a source program into an internal representation

• Parsing Algorithms– LL Parsers: top-down, predictive– LR / LALR Parsers: bottom-up, shift-

reduce

Motivation

• The common approach to create parsers is through compiler-compiler, or parser generator

• Each parser generator is designed for a specific programming language. There is no consistent parser generator– Different grammatical notations– Features and interfaces of tools vary in both the look

and the behavior

• Design and implement a generalized parsing system that supports development of multiple programming languages

• Offer a consistent development environment for the language developers

• Grammar Oriented Language Developer.

• Separating the component that generates parse tables for a target grammar from the component that does the actual parsing.

• Support the full Unicode character set.

• Include a set of tools that can aid language development process.

System Structure

Builder– Analyzes a target grammar and creates DFA and

LALR parse tables– These tables are saved to a Compiled Grammar

Table file

Compiled Grammar Table file– Intermediary between the Builder and the Engine– The file format is platform independent– Format is designed to be very easy to read and

extend in future versions

Engine– Reads the tables & parses the source text – Can be implemented in different programming

languages – as needed

Development Flow

1. Grammar is defined and loaded– Any text editor can be used

2. Builder– Grammar is analyzed and errors

reported– The parse tables are created and saved

to .cgt file

3. Engine– Reads the tables, parses the source

string, and produces parsing results– Can be implemented in different

programming languages – as needed

The Builder

• GOLD meta-language• Compiled grammar table (.cgt) file• Skeleton program creation for the Engine from

program templates• Interactive source string testing• Display of various parse table information• Export parse tables to a web page, XML file, or

formatted text

GOLD Meta-Language

• The GOLD Meta-Language is used to define a target grammar

• It must not contain features that are programming language dependent

• Its notation is very close to the standards

• It supports all language attributes (including those which cannot be specified using BNF or regular expressions)

GOLD Meta-Language (contd.)

• Format – Parameters are used to specify attributes about the

grammar– Character Sets are used to define the character

domain for terminals– Terminals are defined using regular expressions– Rules are defined using Backus-Naur Form

Defining Parameters

• Used for Name, Author, Case Sensitive, Start Rule, ....

• Parameter names are delimited by double quotes

• Parameters– "Name", "Author", "Version", "About" are

informative– "Start Symbol" specifies the initial / start

rule in the grammar

Parameters

"Name", "Version", "Author", "About"Informative fields. These have no effect on table generation.

"Case Sensitive"If set to True, the system will construct case sensitive tokenizer tables.

"Character Mapping"Some characters overlap ordinal values between ANSI and Unicode. If set the ANSI, the system will populate both.

"Auto Whitespace"If not set to False, the system will automatically define a terminal to accept whitespace.

"Start Symbol"The initial/start rule of the grammar. This parameter is required.

Example Parameters

"Name" = 'My Programming Language'

"Version" = '1.0 beta'

"Author" = 'John Q. Public'

"About" = 'This is a test declaration.'

| 'Multiple lines are available'

| 'by using the "pipe" symbol'

"Case Sensitive" = 'False'

"Start Symbol" = <Statement>

Defining Sets

• Character sets are used to aid the construction of regular expressions used to define terminals

• Literal sets of characters are delimited using ‘[’ and ‘]’

• Names of user-defined sets are delimited by ‘{’ and ‘}’

• Sets can be defined by adding and subtracting previously declared sets

Example Sets

{Bracket} = [']'] ]

{Quote} = [''] '

{Vowels} = [aeiou] aeiou

{Vowels 2} = {Vowels} + [y] aeiouy

{Set 1} = [abc] abc

{Set 2} = {Set 1} + [12] - [c] ab12

{Set 3} = {Set 2} + {Digit} ab0123456789

{Hex Char} = {Digit} + [ABCDEF] 0123456789ABCDEF

Pre-defined Character Sets

• There are many sets of characters which are not accessible via keyboard, or so commonly used that it would be repetitive and time-consuming to redefine in each grammar

• GOLD meta-language contains a collection of useful pre-defined sets

• These include sets often used for defining terminals as well as characters not accessible via keyboard

Individual Characters

• Some control characters that cannot be specified on a standard keyboard

Commonly used Character Sets

{Digit}

{Letter}

{Alphanumeric}

{Printable}

{Whitespace}

{Letter Extended}

{Printable Extended}

{ANSI Mapped}

{ANSI Printable}

Unicode Character Sets

• GOLD meta-language contains 43 pre-defined Unicode character sets

• The names of those sets are based on standard names of the Unicode Consortium

Comments

• GOLD meta-language allows both line comments and block comments

Defining Terminals

• Terminals are used to define reserved words, symbols, and recognized patterns (identifiers) in a grammar

• Each terminal is defined using a regular expression which is used to construct the Deterministic Finite Automata used by the tokenizer

• Implicit declaration of frequently used reserved words and symbols

Example Terminals

Example1 = a b c* ab, abc, abcc, abccc, ...

Example2 = a b? c abc, ac

Example3 = a|b|c a, b, c

Example4 = a[12]*b ab, a1b, a2b, a12b, a21b, ...

Example5 = {Letter}+ cat, dog, Sacramento, ...

ListFunction = c[ad]+r car, cdr, caar, cadr, ...

Defining Rules

• Use Backus-Naur Form• Nonterminals are delimited by angle brackets <

and >• Terminals are delimited by single quotes or not

delimited at all

Example: Lists

• Lists are specified using recursive rules

Identifier = {Letter}{Alphanumeric}*

<List Item> ::= Identifier

Recursion

Example: Optional Rules

• Optional rules are specified with a production containing no terminals

• This allows the developer to both specify a list containing 0 or more members

<Quote> ::= ''

| Optional Rule

zero or more

"Name" = 'LISP'

"Author" = 'John McCarthy'

"Version" = 'Minimal'

"About" = 'LISP organizes ALL data around "lists".'

"Start Symbol" = <s-Expr>

{Atom Char} = {Printable} - {Whitespace} - [()"\'']

Atom = ( {Atom Char} | '\'{Printable} )+

<s-Expr> ::= <Quote> Atom

| <Quote> '(' <Series> ')'

| <Quote> '(' <s-Expr> '.' <s-Expr> ')'

<Quote> ::= ''

Example: LISP Grammar

"Name" = 'LISP'"Name" = 'LISP'

"Author" = 'John McCarthy'"Author" = 'John McCarthy'

"Version" = 'Minimal'"Version" = 'Minimal'

"About" = 'LISP organizes ALL data around "lists".' "About" = 'LISP organizes ALL data around "lists".'

"Start Symbol" = <s-Expr>"Start Symbol" = <s-Expr>

<Quote> ::= ''

Parameters

Initial Rule

"Name" = 'LISP'

{Atom Char} = {Printable} - {Whitespace} - [()"\'']{Atom Char} = {Printable} - {Whitespace} - [()"\'']

<Quote> ::= ''

Set Definition

Set Literal

"Name" = 'LISP'

Atom = ( {Atom Char} | '\'{Printable} )+ Atom = ( {Atom Char} | '\'{Printable} )+

<Quote> ::= ''

Terminal Definition

"Name" = 'LISP'

<s-Expr> ::= <Quote> Atom <s-Expr> ::= <Quote> Atom

| <Quote> '(' <Series> ')' | <Quote> '(' <Series> ')'

| <Quote> '(' <s-Expr> '.' <s-Expr> ')'| <Quote> '(' <s-Expr> '.' <s-Expr> ')'

<Quote> ::= ''<Quote> ::= ''

Optional Rule

RecursiveRule

Compiled Grammar Table File

• A file format designed to store parse tables and other information generated by the Builder

• Design considerations– Easy to implement on different platforms– Flexibility for data structures to be added or

expanded– Room for future growth (additional new types of data)

.cgt File Structure

• The file consists of a number of records• Each record contains a number of entries

.cgt Record

• The header contains name and version info• A record has the following format

Parameter Record

• Parameter record which only occurs once in the .cgt file. It contains information about the grammar as well as attributes that affect how the grammar functions. The record is preceded by a byte field contains the value 80, the ASCII code for the letter 'P'.

Table Size Record

• Table size record : that appears before any records containing information about symbols, sets, rules or state table information. The first field of the record contains a byte with the value 84 - the ASCII code for the letter 'T’ Each value contains the total number of objects for each of the listed tables

Other Types of Records

• Character set table member• Symbol table member• Initial states (for both DFA and LALR)• Rule table member• DFA state table member• LALR state table member

An Example cgt File

• An example grammar "Name" = 'Example'

"Version" = '1.0‘

"Author" = 'Devin Cook'

"About" = 'N/A'

"Start Symbol" = <Stms>

| <Stm>

<Stm> ::= if <Exp> then <Stms> end

| Read Id

| Write <Exp>

| Id '-' <Exp>

Table Content

• Symbol Table========================================Symbol Table========================================Index Name----- ------------0 (EOF)1 (Error)2 (Whitespace)3 '-'4 '+'5 end6 Id7 if8 Read9 then10 Write11 <Exp>12 <Stm>13 <Stms>

Table Content (2)

• Rules========================================

========================================

Index Name ::= Definition

----- ------ --- ------------------------

0 <Stms> ::= <Stm> <Stms>

1 <Stms> ::= <Stm>

2 <Stm> ::= if <Exp> then <Stms> end

3 <Stm> ::= Read Id

4 <Stm> ::= Write <Exp>

5 <Exp> ::= Id '+' <Exp>

6 <Exp> ::= Id '-' <Exp>

7 <Exp> ::= Id

Table Content (3)

• Character Set Table========================================

Character Set Table

========================================

Index Characters

----- ---------------------------------

0 {HT}{LF}{VT}{FF}{CR}{Space}{NBSP}

Table Content (3)

• DFA states========================================DFA States========================================Index Description Character Set-------- ------------------- -------------0 Goto 1 0 Goto 2 1 Goto 3 2 Goto 4 3 Goto 7 4 Goto 10 5 Goto 14 6 Goto 18 71 Goto 1 0 Accept (Whitespace)…………

Table Content (4)

• LALR states========================================

LALR States

========================================

Index Configuration/Action

-------- ------------------------------------

0 if Shift 1

Read Shift 9

Write Shift 11

<Stm> Goto 13

<Stms> Goto 17

1 <Stm> ::= if · <Exp> then <Stms> end

Id Shift 2

<Exp> Goto 7

…………

cgt File for the grammar

• To illustrate, only one of each record type is included

'b' 'T'

'I' 14

Symbol Table

'I' 13

Character SetTable

Rule Table

'I' 23

DFA TableTable Counts

'I' 18

LALR Table

'b' 'S'

IndexSymbol

CharacterSet

Characters

'b' 'R'

IndexRule

'I' 13

Nonterminal

(Empty)

'I' 12

Symbol 0

'I' 13

Symbol 1

'b' 'D'

IndexDFA State

Accept Index

(Empty)

Character Set Index0

Target Index0

Accept State

(Empty)0

'b' 'L'

IndexLALR State

(Empty)

Action0

Target0

'E''I' 9

Symbol Index 0 (Empty)0

Parameters

Example

Version

Author

Devin Cook

CaseSensitive

Start Symbol

DFAInitial States LALR

'b' 'I'

The Remaining Builder Features

• Besides meta-language and .cgt file, – Skeleton program creation for the Engine from

program templates– Interactive source string testing– Display of various parse table information– Export parse tables to a web page, XML file, or

formatted text

Online Help

Application Layout

Status Message

Grammar Editor

Next Button

Toolbar

Program Templates

• When developing the Engine which is interacting with tables of rules and symbols in the .cgt file, manually typing constant definitions can be tedious and problematic

• Program templates are designed to help automate the Engine development

• The Builder can use a program template to create a “skeleton program” for an implementation of the Engine

Program Templates (contd.)

• Skeleton program contains– Necessary declarations of

constants and variables– Function calls– Case statements, pre-processor

statements– Ready-to-use programs

• Notation designed to not conflict with known languages

• Program templates are saved in a subfolder

Display of Symbol Table

• Symbol table display

Display of Rule Table

• Rule table display

Display of Log Information

• Log info: general information about the number of symbols, which ones were defined implicitly, table counts, and any errors that occur

Display of DFA State Table

• DFA state table

Display of LALR State Table

• LALR state table

Export Parse Tables

• Parse tables can be exported to a web page, formatted text, or an XML file

Web Page Export

• An example of webpage export

A Short Demo

• A simple grammar• ANSI C

The Engine

• Different implementations of the Engine• Object-oriented approach• Its design is centered around the object

of “GOLDParser”, which performs all the parsing logic

• The remaining objects are used for storage or to support GOLDParser object

• Available in: Visual Basic .NET, ANSI C, C#, C++ (MFC), Delphi 5 & 6, Java, Python, Visual Basic 6

Testing and Development

• Extensive tests on the Builder’s algorithms to generate the LALR and DFA tables– Small grammars– Grammars for the real world programming languages

(e.g., ANSI C, BASIC, COBOL, LISP, Smalltalk, SQL, Visual Basic .NET, HTML, XML)

• A Visual Basic 6 version of the Engine was developed as an integral part of the GOLD system and was tested

Comparison

• Yacc: for C or C++ on UNIX platform• ANTLR: OO parser generator that works for C++,

C#, and Java• Bison: Yacc compatible• Elkhound: parser generator that is based on

generalied LR algorithm• GENOA: framework for code analysis tools that

has a parsing front end

Free Parsing Systems

Language GOLD YACC ANTLR Grammatica

ANSI C C++ C# Delphi 5 & 6 Java Python Visual Basic 5 & 6 Visual Basic .NET All .NET Languages All ActiveX Languages

Benefits of GOLD

• It supports development of multiple programming languages and the full Unicode character set

• It has a set of development tools• Its meta-language is easy to understand and its

Builder GUI is easy to use

Contributors to Different Engines

Manuel Astudillo C++ implementation

Max Battcher Recompiled .NET Source to a DLL

Matthew Hawkins Java implementation

Justin Holmes ANSI C implementation

Ibrahim Khachab Modified Delphi version

Marcus Klimstra C# implementation

Milosz A. Krajewski Python implementation

Alexandre Rai Delphi implementation

Eylem Ugurel C++ implementation

Martin van der Geer Delphi implementation

Robert van Loenhout C# implementation

Reggie Wilbanks Ported the Engine to Visual Basic .NET

Website

• The URL for the GOLD website

http://www.devincook.com/goldparser

• On average, approximately 3000 copies of the Builder application are downloaded per month

• Latest news: known bugs, workarounds, new releases

• Contributor section• Online documentation

Future Work

• Port the Builder to UNIX and Linux

• Enhancement to the meta grammar

Gold Parser

Documents