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 JavaCC: JJTree README




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.