:index:`Introduction to ANTLR4`
        
Introduction to ANTLR4
======================

Preparing the environment
-------------------------

First of all, let's define some PATHs and variables that will ease the execution of the required tools.

Execute (just once):

::

   cat /assig/$USER/cl/tcshrc.CL-GRAU.antlr4 >> ~/.tcshrc && source ~/.tcshrc


Session 1
---------

The first session consists of building a calculator able to compute simple aritmethic expressions.

We are provided a base grammar ``Calc.g4``, and different example programs that traverse the generated tree.

Your professor will explain the initial example and how each example works.

You should then finish the calculator adding other operations.

* You will find the examples for this season in folder `/assig/$USER/cl/files/intro.tgz` in FIB inLab server, or you can get it from :download:`here <files/intro.tgz>`.

  
Useful tools for grammar development
------------------------------------

To develop and debug our grammar, it is useful to visualize the parse trees it builds.

Antlr4 provides ``grun``, a java tool able to provide this visualization.

Since ``grun`` is written in java, it requires the java classes for our grammar. Our ``Makefile`` creates only C++ classes, so we will need to compile the java version:
::

   antlr4 myGrammar.g4
   javac *.java

Once this is done, we can run ``grun`` to obtain the tree for a given input:

To display the tree in parenthesized format:
::

   grun myGrammar myInitialSymbol -tree inputfile

To display the tree in graphical format:
::

   grun myGrammar myInitialSymbol -gui inputfile

In both above commands ``inputfile`` may be ommited and typed in ``stdin`` ending with ``ctl-D``