# JavaCC [tm]: README 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 [tm] 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.

    eg4.jjt

    This is a modification of eg3.jjt with the VISITOR option set.  This
    instructs JJTree to insert a jjtAccept() method into all nodes it
    generates, and to produce a visitor class.  The visitor is used to
    dump the tree.

    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.

    trane% jjtree eg1.jjt
    <<< Version and copyright info>>>
    (type "jjtree" with no arguments for help)
    Reading from file eg1.jjt . . .
    Annotated grammar generated successfully in eg1.jj
    trane%

    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.

    trane% javacc eg1.jj
    <<< Version and copyright info>>>
    (type "javacc" with no arguments for help)
    Reading from file eg1.jj . . .
    File "TokenMgrError.java" does not exist.  Will create one.
    File "ParseException.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.
    trane%

    Compile and run the Java program as usual.  The expression is read from the
    standard input (you type in "(a + b) * (c + 1);"):

    trane% javac eg1.java
    trane% 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.
    trane%

    eg2.jjt
    -------

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

    trane% jjtree eg2.jjt
    <<< Version and copyright info>>>
    (type "jjtree" with no arguments for help)
    Reading from file eg2.jjt . . .
    File "Node.java" does not exist.  Will create one.
    File "SimpleNode.java" does not exist.  Will create one.
    File "ASTStart.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
    trane%
    trane% javacc eg2.jj
    <<< Version and copyright info>>>
    (type "javacc" with no arguments for help)
    Reading from file eg2.jj . . .
    File "TokenMgrError.java" does not exist.  Will create one.
    File "ParseException.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.
    trane%
    trane% javac eg2.java
    trane% java eg2
    Reading from standard input...
    (a + b) * (c + 1);
    Start
     Mult
      Add
       Identifier: a
       Identifier: b
      Add
       Identifier: c
       Integer
    Thank you.
    trane%

    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.

    eg3.jjt
    -------

    This example can be run in the same manner as you ran eg2.jjt.

    eg4.jjt
    -------

    This example again can be run in the same manner as you ran eg2.jjt.
    One thing to take care in this case is that you must run jjtree on
    a clean directory (that does not contain previously generated files).
    For example, the file SimpleNode.java is different when the option
    VISITOR is set to true.