The README File for JJTreeExamples

JJTreeExamples

This directory contains some simple JJTree input files intended to
illustrate some of the basic ideas.  All of them are based on an
grammar to recognize arithmetic expressions built out of identifiers
and constants.

eg1.jjt

This example is just the JavaCC grammar, with a little extra code in
the parser's main method to call the dump method on the generated
tree.  It illustrates how the default behavior of JJTree will produce
a tree of non-terminals.

eg2.jjt

This example is the same grammar as eg1.jjt with modifications to
customize the generated tree.  It illustrates how unnecessary
intermediate nodes can be suppressed, and how actions in the grammar
can attach extra information to the nodes.

eg3.jjt

This example is a modification of eg2.jjt with the NODE_DEFAULT_VOID
option set.  This instructs JJTree to treat all undecorated
non-terminals as if they were decorated as #void. The default JJTree
behavior is to treat such non-terminals as if they were decorated
with the name of the non-terminal.


Here are some instructions on how to run the examples and the output
you can expect to see.

eg1.jjt
-------

The only bit of JJTree-specific code is an action in the start
production that dumps the constructed parse tree when the parse is
complete.  It uses JJTree simple mode.

The input file is eg1.jjt.

    adl% Java Compiler Compiler Version 0.6(Beta2) (Tree Builder Version 0.2.3)
    Copyright (c) 1996, 1997 Sun Microsystems Inc.
    (type "jjtree" with no arguments for help)
    Reading from file eg1.jjt . . .
    File "Node.java" does not exist.  Will create one.
    File "SimpleNode.java" does not exist.  Will create one.
    Annotated grammar generated successfully in eg1.jj

JJTree has now generated the JavaCC parser source, as well as Java
source for the parse tree node building classes.  Running JavaCC in
the normal way generates the remaining Java code.

    adl% javacc eg1.jj
    Java Compiler Compiler Version 0.6(Beta2) (Parser Generator)
    Copyright (c) 1996, 1997 Sun Microsystems Inc.
    (type "javacc" with no arguments for help)
    Reading from file eg1.jj . . .
    File "ParseError.java" does not exist.  Will create one.
    File "Token.java" does not exist.  Will create one.
    File "ASCII_CharStream.java" does not exist.  Will create one.
    Parser generated successfully.

Compile and run the Java as usual.  The expression is read from the
standard input, and is terminated by an end of file character.

    adl% javac eg1.java
    adl% java eg1
    Reading from standard input...
    (a + b) * (c + 1)
    Start
     Expression
      AdditiveExpression
       MultiplicativeExpression
	UnaryExpression
	 Expression
	  AdditiveExpression
	   MultiplicativeExpression
	    UnaryExpression
	     Identifier
	   MultiplicativeExpression
	    UnaryExpression
	     Identifier
	UnaryExpression
	 Expression
	  AdditiveExpression
	   MultiplicativeExpression
	    UnaryExpression
	     Identifier
	   MultiplicativeExpression
	    UnaryExpression
	     Integer
    Thank you.

eg2.jjt
-------

This is a modification of the first example to illustrate how the
parse tree can be customized:

    adl% jjtree eg2.jjt
    Java Compiler Compiler Version 0.6(Beta2) (Tree Builder Version 0.2.3)
    Copyright (c) 1996, 1997 Sun Microsystems Inc.
    (type "jjtree" with no arguments for help)
    Reading from file eg2.jjt . . .
    File "Node.java" does not exist.  Will create one.
    File "ASTStart.java" does not exist.  Will create one.
    File "SimpleNode.java" does not exist.  Will create one.
    File "ASTAdd.java" does not exist.  Will create one.
    File "ASTMult.java" does not exist.  Will create one.
    File "ASTInteger.java" does not exist.  Will create one.
    Annotated grammar generated successfully in eg2.jj
    adl% javacc eg2.jj
    Java Compiler Compiler Version 0.6(Beta2) (Parser Generator)
    Copyright (c) 1996, 1997 Sun Microsystems Inc.
    (type "javacc" with no arguments for help)
    Reading from file eg2.jj . . .
    File "ParseError.java" does not exist.  Will create one.
    File "Token.java" does not exist.  Will create one.
    File "ASCII_CharStream.java" does not exist.  Will create one.
    Parser generated successfully.
    adl% javac eg2.java
    adl% java eg2
    Reading from standard input...
    (a + b) * (c + 1)
    Start
     Mult
      Add
       MyID: a
       MyID: b
      Add
       MyID: c
       Integer
    Thank you.

Look at eg2.jjt to see how node annotations can be used to restructure
the parse tree, and at ASTMyID.java to see how you can write your own
node classes that maintain more information from the input stream.