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GOLD: A Grammar Oriented Parsing System Devin Cook and Du Zhang Department of Computer Science California State University Sacramento, 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

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GOLD: A Grammar Oriented Parsing SystemDevin Cook and Du ZhangDepartment of Computer ScienceCalifornia State UniversitySacramento, CA 95819-6021

SEKE 2004

  • 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
  • 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
System Structure


  • 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


  • Reads the tables & parses the source text
  • Can be implemented in different programming languages – as needed
development flow
Development Flow
  • Grammar is defined and loaded
    • Any text editor can be used
  • Builder
    • Grammar is analyzed and errors reported
    • The parse tables are created and saved to .cgt file
  • Engine
    • Reads the tables, parses the source string, and produces parsing results
    • Can be implemented in different programming languages – as needed
the builder
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
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
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
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
example parameters
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
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
pre defined character sets
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
Individual Characters
  • Some control characters that cannot be specified on a standard keyboard
commonly used character sets
Commonly used Character Sets






{Letter Extended}

{Printable Extended}

{ANSI Mapped}

{ANSI Printable}

unicode character sets
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
  • GOLD meta-language allows both line comments and block comments
defining terminals
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
defining rules
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
Example: Lists
  • Lists are specified using recursive rules


example optional rules
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

zero or more

Optional Rule

example lisp grammar1
Example: LISP Grammar


Initial Rule

example lisp grammar2
Example: LISP Grammar

Set Definition

Set Literal

example lisp grammar3
Example: LISP Grammar

Terminal Definition

example lisp grammar4
Example: LISP Grammar




Optional Rule

compiled grammar table file
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
.cgt File Structure
  • The file consists of a number of records
  • Each record contains a number of entries
cgt record
.cgt Record
  • The header contains name and version info
  • A record has the following format
parameter record
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
  • 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
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 cgt File
  • An example grammar

"Name" = 'Example'

"Version" = '1.0‘

"Author" = 'Devin Cook'

"About" = 'N/A'

"Start Symbol" = <Stms>

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

| <Stm>

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

| Read Id

| Write <Exp>

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

| Id '-' <Exp>

| Id

table content
Table Content
  • Symbol Table


Symbol Table


Index Name

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

0 (EOF)

1 (Error)

2 (Whitespace)

3 '-'

4 '+'

5 end

6 Id

7 if

8 Read

9 then

10 Write

11 <Exp>

12 <Stm>

13 <Stms>

table content 2
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
Table Content (3)
  • Character Set Table


Character Set Table


Index Characters

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

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

1 +

2 -

3 Ee

4 Ii

5 Rr

6 Tt

7 Ww

8 Nn

9 Dd

10 Ff

11 Aa

12 Hh

table content 31
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 7

1 Goto 1 0

Accept (Whitespace)


table content 4
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
cgt File for the grammar
  • To illustrate, only one of each record type is included
the remaining builder features
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
application layout
Application Layout

Online Help


Grammar Editor

Next Button

Status Message

program templates
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
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
Display of Symbol Table
  • Symbol table display
display of rule table
Display of Rule Table
  • Rule table display
display of log information
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
export parse tables
Export Parse Tables
  • Parse tables can be exported to a web page, formatted text, or an XML file
web page export
Web Page Export
  • An example of webpage export
a short demo
A Short Demo
  • A simple grammar
  • ANSI C
the engine
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
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
  • 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
benefits of gold
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
  • The URL for the GOLD website

  • 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
Future Work
  • Port the Builder to UNIX and Linux
  • Enhancement to the meta grammar