Antlr - Parse Tree (AST)

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The tree parser is an AST that is created by the parser from a text input.




with grun, see the -tree of -gui option of


grun grammar startRule -tree
grun grammar startRule -gui

Type your text and end with a End of File character (Ctrl+Z or Ctrl+D)


With the idea plugin:

  • right click on the line of the start rule
  • start to type a text to see the tree

Antlr Idea Plugin



Example from the getting started with an Hello.g4 grammar file that was generated in:

  • a lexer file called
  • a parser file called

The grammar below will parse every hello [a-z]+ text.

grammar Hello;
r  : 'hello' ID ;   // Top parser rule of the tree
ID : [a-z]+ ;      
WS : [ \t\r\n]+ -> skip ;

To build a tree, you need to:

ANTLRInputStream input = new ANTLRInputStream("hello nico");
  • Build the lexer from the input
HelloLexer lexer = new HelloLexer(input);
  • Wrap the lexer into a stream of tokens CommonTokenStream (The parser can then read this stream back and forth)
CommonTokenStream tokens = new CommonTokenStream(lexer);
  • Create a parser that will build the tree
HelloParser parser = new HelloParser(tokens);
  • Finally, you can build the tree (a ParseTree) from the parser rule called r (present in the grammar file and generated in the parser as a function)
ParseTree tree = parser.r();    
System.out.println(tree.toStringTree(parser)); // print LISP-style tree

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Antlr - (Grammar|Lexicon) (g4)

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Antlr - (Lexical) Rule

in Antlr. Antlr has two types of rule: Name Case Type Description Example from the getting started uppercase letter lexer rule (known as Token name, they defines the token that the lexer...
Card Puncher Data Processing
Antlr - Generated class

From the grammar The lexer rules will create the lexer class The parser rules will create the parser class The classes generated will contain a method for each rule in the grammar. See from...
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Antlr - Getting Started (Hello World)

A getting started page that brings you in the world of Antlr. antlr/antlr4/blob/master/doc/getting-started.mdantlr4 getting-started Create a grammar file called Hello.g4 and define the grammar...
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Antlr - Idea Plugin

The Idea plugin is a plugin for Idea that install the Antlr tool. Create a grammar file with the extension g4 and Idea should propose you to install the Antlr...
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Antlr - Parse Tree Listener

The parse tree listener (or listener) is a class that implements callback methods that are called by the parser when it creates the parse tree. You can overwrite this class to get information when the...
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Antlr - Parse Tree Visitor

The in Antlr that will visit the parse tree in a depth-first search order In a visitor, you can: control the order of visite return data from the function Use mainly when the code is spread around...
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Antlr - Parser

in Antlr. The parser is a generated class that is build from the grammar (specifically from the parser rule of the grammar). The job of the parser is to create a parse tree from: a parser start rule...
Card Puncher Data Processing
Antlr - Parser Rule

in Antlr. Parser rule is the second type of rule for Antlr. They begin with a lowercase letter. The lexer rules specify the tokens whereas the parser rules specify the tree. URL URI See ...
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Antlr - Start Rule

A start rule is the rule engaged first by the parser to create the tree. Any rule in the grammar can act as a start rule. ...

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