/AntlrProject

Learn Antlr4

Primary LanguageJava

Antlr 4

Usage

❯ java -jar build/libs/AntlrProject-all-1.0-SNAPSHOT.jar  testCases/test3.txt
Main Class of Antlr.libs/AntlrProject-all-1.0-SNAPSHOT.jar  testCases/test3.txt
i is 5
j is 7
i + j is 12
i + j * 3 is 26
i + j + 3 is 15
10 is 10

Install Antlr

  1. Download Antlr-4.12.0 jar file from antlr.org

  2. Move downloaded jar to /usr/local/lib

  3. Add configs to my .zshrc as following

    # ANTLR4
alias antlr4='java -jar /usr/local/lib/antlr-4.12.0-complete.jar'
export CLASSPATH="/usr/local/lib/antlr-4.12.0-complete.jar:$CLASSPATH"
alias grun='java org.antlr.v4.gui.TestRig'

  4. Verification Installation

     ❯ grun
 java org.antlr.v4.gui.TestRig GrammarName startRuleName
 [-tokens] [-tree] [-gui] [-ps file.ps] [-encoding encodingname]
 [-trace] [-diagnostics] [-SLL]
 [input-filename(s)]
 Use startRuleName='tokens' if GrammarName is a lexer grammar.
 Omitting input-filename makes rig read from stdin.
 ❯
 ❯ antlr4
 ANTLR Parser Generator  Version 4.12.0
 -o ___              specify output directory where all output is generated
 -lib ___            specify location of grammars, tokens files
 -atn                generate rule augmented transition network diagrams
 -encoding ___       specify grammar file encoding; e.g., euc-jp
 -message-format ___ specify output style for messages in antlr, gnu, vs2005
 -long-messages      show exception details when available for errors and warnings
 -listener           generate parse tree listener (default)
 -no-listener        don't generate parse tree listener
 -visitor            generate parse tree visitor
 -no-visitor         don't generate parse tree visitor (default)
 -package ___        specify a package/namespace for the generated code
 -depend             generate file dependencies
 -D<option>=value    set/override a grammar-level option
 -Werror             treat warnings as errors
 -XdbgST             launch StringTemplate visualizer on generated code
 -XdbgSTWait         wait for STViz to close before continuing
 -Xforce-atn         use the ATN simulator for all predictions
 -Xlog               dump lots of logging info to antlr-timestamp.log
 -Xexact-output-dir  all output goes into -o dir regardless of paths/package

  5. Add Antlr Plugin to IntelliJ

    1. Identify .g4 files and can preview parse Tree for given input

  6. Add Antlr dependencies for the Java Project

    https://docs.gradle.org/current/userguide/antlr_plugin.html

    plugins {
    id 'antlr'
}

dependencies {
   antlr 'org.antlr:antlr4:4.12.0' // use antlr version 4.
}

generateGrammarSource {
   maxHeapSize = "64m"
   arguments += ["-visitor"] // Add visitor classes
   outputDirectory = file('src/main/java/com/neil3d2y/antlr/generated')
}

Workflow of Using Antlr

  1. .g4 to define grammar

  2. ANTLR command line tool read .g4 and generates

    (-visitor)

    1. Parser.java
    2. Lexer.java
    3. Visitor classes

    Another Way: (-no-visitor)

    1. Parser.java
    2. Lexer.java

    Third Way:

    1. Parser.java
    2. Lexer.java
    3. Listeners for GUI apps

  3. My Own Java Classes use above generated Classes

Parser Generator

Build Model Classes for Each Element in the Grammar

  • Number
  • Variable
  • Multiplication
  • Addition

WHY do we need to define these models classes instead of manipulating the parse tree generated by Antlr?

To have 100% control on the AST.

  1. Every internal node of parse tree (expr, decl) should correspond to a Model Class.
Parse Tree Internal Node Model Class
decl VariableDeclaration.class
expr (+) Addition.class
expr (*) Multiplication.class

  1. We use visitor pattern here

    For each Model Class we will also have one corresponding Visitor Class / Function that converts the internal node to the Model Class.

    Visitor Design Pattern Link

    • Behavioral Design pattern
    • Use when we have to perform an operation on a group of similar kind of objects.

Compiler Knowledge

https://pediaa.com/what-is-the-difference-between-lex-and-yacc/

What is the diff between Yacc and Lex

The main difference between Lex and Yacc is that Lex is a lexical analyzer which converts the source program into meaningful tokens while Yacc is a parser that generates a parse tree from the tokens generated by Lex.