ANTLR3 Tutorials: Five minute introduction to ANTLR 3 - go-sqlparser/current GitHub Wiki
Five minute introduction to ANTLR 3
Created by Former user (Deleted)
Last updated: Mar 30, 2012 by Former user (Deleted)
What is ANTLR 3?
ANTLR - ANother Tool for Language Recognition - is a tool that is used in the construction of formal language software tools (or just language tools) such as translators, compilers, recognizers and, static/dynamic program analyzers. Developers use ANTLR to reduce the time and effort needed to build and maintain language processing tools. In common terminology, ANTLR is a compiler generator or compiler compiler (in the tradition of tools such as Lex/Flex and Yacc/Bison) and it is used to generate the source code for language recognizers, analyzers and translators from language specifications. ANTLR takes as its input a grammar - a precise description of a language augmented with semantic actions - and generates source code files and other auxiliary files. The target language of the generated source code (e.g. Java, C/C++, C#, Python, Ruby) is specified in the grammar.
Software developers and language tool implementors can use ANTLR to implement Domain-Specific Languages, to generate parts of language compilers and translators, or even to help them build tools that parse complex XML.
As stated above, ANTLR 3 generates the source code for various tools that can be used to recognize, analyze and transform input data relative to a language that is defined in a specified grammar file. The basic types of language processing tools that ANTLR can generates are Lexers (a.k.a scanners, tokenizers), Parsers and, TreeParsers (a.k.a tree walkers, c.f. visitors).
What exactly does ANTLR 3 do?
ANTLR reads a language description file called a grammar and generates a number of source code files and other auxiliary files. Most uses of ANTLR generates at least one (and quite often both) of these tools:
- A Lexer: This reads an input character or byte stream (i.e. characters, binary data, etc.), divides it into tokens using patterns you specify, and generates a token stream as output. It can also flag some tokens such as whitespace and comments as hidden using a protocol that ANTLR parsers automatically understand and respect.
- A Parser: This reads a token stream (normally generated by a lexer), and matches phrases in your language via the rules (patterns) you specify, and typically performs some semantic action for each phrase (or sub-phrase) matched. Each match could invoke a custom action, write some text via StringTemplate, or generate an Abstract Syntax Tree for additional processing.
ANTLR's Abstract Syntax Tree (AST) processing is especially powerful. If you also specify a tree grammar, ANTLR will generate a Tree Parser for you that can contain custom actions or StringTemplate output statements. The next version of ANTLR (3.1) will support rewrite rules that can be used to express tree transformations.
Most language tools will:
- Use a Lexer and Parser in series to check the word-level and phrase-level structure of the input and if no fatal errors are encountered, create an intermediate tree representation such as an Abstract Syntax Tree (AST),
- Optionally modify (i.e tranform or rewrite) the intermediate tree representation (e.g. to perform optimizations) using one or more Tree Parsers, and
- Produce the final output using a Tree Parser to process the final tree representation. This might be to generate source code or other textual representation from the tree (perhaps using StringTemplate) or, performing some other custom actions driven by the final tree representation.
Simpler language tools may omit the intermediate tree and build the actions or output stage directly into the parser. The calculator shown below uses only a Lexer and a Parser.
ANTLR, Then and Now
ANTLR 3 is the latest version of a language processing toolkit that was originally released as PCCTS in the mid-1990s. As was the case then, this release of the ANTLR toolkit advances the state of the art with its new LL
parsing engine. ANTLR provides a framework for the generation of recognizers, compilers, and translators from grammatical descriptions. ANTLR grammatical descriptions can optionally include action code written in what is termed the target language (i.e. the implementation language of the source code artifacts generated by ANTLR).
When it was released, PCCTS supported C as its only target language, but through consulting with NeXT Computer, PCCTS gained C++ support after 1994. PCCTS's immediate successor was ANTLR 2 and it supported Java, C# and Python as target languages in addition to C++.
Target languages
ANTLR 3 already supports Java, C#, Objective C, C, Python and Ruby as target languages. Support for additional target languages including C++, Perl6 and Oberon (yes, Oberon) is either expected or already in progress. This is all due in part to the fact that it is much easier to add support for a target language (or customize the code generated by an existing target) in ANTLR 3.
Why should I use ANTLR 3?
Because it can save you time and resources by automating significant portions of the effort involved in building language processing tools. It is well established that generative tools such as compiler compilers have a major, positive impact on developer productivity. In addition, many of ANTLR v3's new features including an improved analysis engine, its significantly enhanced parsing strength via LL parsing with arbitrary lookahead, its vastly improved tree construction rewrite rules and the availability of the simply fantastic AntlrWorks IDE offers productivity benefits over other comparable generative language processing toolkits.
How do I use ANTLR 3?
1. Get ANTLR 3
Download and install ANTLR 3 from the ANTLR website.
2. Run ANTLR 3 on a simple grammar
2.1 Create a simple grammar
Java
grammar SimpleCalc;
tokens {
PLUS = '+' ;
MINUS = '-' ;
MULT = '*' ;
DIV = '/' ;
}
@members {
public static void main(String[] args) throws Exception {
SimpleCalcLexer lex = new SimpleCalcLexer(new ANTLRFileStream(args[0]));
CommonTokenStream tokens = new CommonTokenStream(lex);
SimpleCalcParser parser = new SimpleCalcParser(tokens);
try {
parser.expr();
} catch (RecognitionException e) {
e.printStackTrace();
}
}
}
/*------------------------------------------------------------------
* PARSER RULES
*------------------------------------------------------------------*/
expr : term ( ( PLUS | MINUS ) term )* ;
term : factor ( ( MULT | DIV ) factor )* ;
factor : NUMBER ;
/*------------------------------------------------------------------
* LEXER RULES
*------------------------------------------------------------------*/
NUMBER : (DIGIT)+ ;
WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+ { $channel = HIDDEN; } ;
fragment DIGIT : '0'..'9' ;
C#
Note: language=CSharp2 with ANTLR 3.1; ANTLR 3.0.1 uses the older CSharp target
grammar SimpleCalc;
options {
language=CSharp2;
}
tokens {
PLUS = '+' ;
MINUS = '-' ;
MULT = '*' ;
DIV = '/' ;
}
@members {
public static void Main(string[] args) {
SimpleCalcLexer lex = new SimpleCalcLexer(new ANTLRFileStream(args[0]));
CommonTokenStream tokens = new CommonTokenStream(lex);
SimpleCalcParser parser = new SimpleCalcParser(tokens);
try {
parser.expr();
} catch (RecognitionException e) {
Console.Error.WriteLine(e.StackTrace);
}
}
}
/*------------------------------------------------------------------
* PARSER RULES
*------------------------------------------------------------------*/
expr : term ( ( PLUS | MINUS ) term )* ;
term : factor ( ( MULT | DIV ) factor )* ;
factor : NUMBER ;
/*------------------------------------------------------------------
* LEXER RULES
*------------------------------------------------------------------*/
NUMBER : (DIGIT)+ ;
WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+ { $channel = Hidden; } ;
fragment DIGIT : '0'..'9' ;
Objective-C
To be written. Volunteers?
grammar SimpleCalc;
options
{
language=ObjC;
}
OR : '||' ;
C
grammar SimpleCalc;
options
{
language=C;
}
tokens
{
PLUS = '+' ;
MINUS = '-' ;
MULT = '*' ;
DIV = '/' ;
}
@members
{
#include "SimpleCalcLexer.h"
int main(int argc, char * argv[])
{
pANTLR3_INPUT_STREAM input;
pSimpleCalcLexer lex;
pANTLR3_COMMON_TOKEN_STREAM tokens;
pSimpleCalcParser parser;
input = antlr3AsciiFileStreamNew ((pANTLR3_UINT8)argv[1]);
lex = SimpleCalcLexerNew (input);
tokens = antlr3CommonTokenStreamSourceNew (ANTLR3_SIZE_HINT, TOKENSOURCE(lex));
parser = SimpleCalcParserNew (tokens);
parser ->expr(parser);
// Must manually clean up
//
parser ->free(parser);
tokens ->free(tokens);
lex ->free(lex);
input ->close(input);
return 0;
}
}
/*------------------------------------------------------------------
* PARSER RULES
*------------------------------------------------------------------*/
expr : term ( ( PLUS | MINUS ) term )*
;
term : factor ( ( MULT | DIV ) factor )*
;
factor : NUMBER
;
/*------------------------------------------------------------------
* LEXER RULES
*------------------------------------------------------------------*/
NUMBER : (DIGIT)+
;
WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+
{
$channel = HIDDEN;
}
;
fragment
DIGIT : '0'..'9'
;
Python
grammar SimpleCalc;
options {
language = Python;
}
tokens {
PLUS = '+' ;
MINUS = '-' ;
MULT = '*' ;
DIV = '/' ;
}
@header {
import sys
import traceback
from SimpleCalcLexer import SimpleCalcLexer
}
@main {
def main(argv, otherArg=None):
char_stream = ANTLRFileStream(sys.argv[1])
lexer = SimpleCalcLexer(char_stream)
tokens = CommonTokenStream(lexer)
parser = SimpleCalcParser(tokens);
try:
parser.expr()
except RecognitionException:
traceback.print_stack()
}
/*------------------------------------------------------------------
* PARSER RULES
*------------------------------------------------------------------*/
expr : term ( ( PLUS | MINUS ) term )* ;
term : factor ( ( MULT | DIV ) factor )* ;
factor : NUMBER ;
/*------------------------------------------------------------------
* LEXER RULES
*------------------------------------------------------------------*/
NUMBER : (DIGIT)+ ;
WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+ { $channel = HIDDEN; } ;
fragment DIGIT : '0'..'9' ;