## Using Jacc

These are instructions on how to use `Jacc`.

### Accessing the package

Copy the file `jacc.zip` to wherever you deem appropriate in your file system, unzip it, and enable your class path to access the unzipped jar file.

Then, invoking `Jacc` on a grammar file from a terminal console is done by typing:

    java ilog.language.syntax.Jacc <grammar file>

Or, more conveniently by defining a command for invoking `Jacc`; e.g., in UNIX:

    alias jacc java ilog.language.syntax.Jacc

so that one need only type:

    jacc <grammar file>

to invoke it. Options available to `Jacc` are described by specifying no arguments. Thus:

    jacc

    Usage: jacc [options] grammar_file(s)

    Option   (Default)    Description
    ------   ---------    -----------
    -doc     ()           generate only the grammar documentation
    -i       ()           tolerate an incomplete grammar (no parser is generated)
    -n       ()           do not generate the parser
    -o       (System.out) redirect the log to the specified file
    -e       (System.err) redirect errors to the specified file
    -p       (Parser)     parser name (default: grammar="Foo.grm" => parser="FooParser.java")
    -rrp     ()           resolve R/R conflicts based on precedence (dangerous!)
    -s       (\)          file separator character
    -m       (1000)       max number of instructions in parser initialization method
    -trail   (100)        max size of trail history (for dynamic parsing)
    -v       (1)          information verbosity (number between 0 and 4)
    -amb     ()           allow ambiguous actions (for dynamic parsing)
    -choices (10)         max size of choice history (for dynamic parsing)

### Using the package

We illustrate the process on an example: that of a simple arithmetic calculator. This example defines an interactive java program that reads input from the terminal. The calculator repeatedly prompts the user, reads an input, and prints the parse tree followed by the evaluation result. Inputs are either arithmetic expressions using the four operations (`+`, `-`, `*`, and `/`), numbers, and identifiers. A definition is of form `id = ex` where `id` is an identifier, and `ex` is an expression. Expressions and definitions are terminated with a semicolon (`;`). To exit, one types the command `exit;`.

A `Jacc` grammar for such a calculator is specified in the file Calculator.grm. To generate the parser corresponding to this grammar, one simply runs `Jacc` as indicated above on the grammar file. In our case:

    % jacc Calculator
    *** Reading grammar in file Calculator.grm ...
    *** Starting grammar analysis ...
    *** Grammar analysis completed in 70 ms.
    *** Building parsing tables ...
    *** Writing parser file CalculatorParser.java
    *** Parser generation completed in 90 ms.
    *** Total processing time: 240 ms.

This generates a parser for the specified grammar as a java program called CalculatorParser.java.

In order to have a complete system, we need a tokenizer and a driver.

Our calculator grammar uses a tokenizer class called `CalculatorTokenizer`. A possible implementation for it is shown in the file CalculatorTokenizer.java.

A simple driver for the complete calculator is shown in the file CalculatorMain.java.

Then, all one must do is compile the three files (parser, tokenizer, and driver) using `javac`, and the calculator is ready by executing its driver. To wit:

    % java CalculatorMain
    *** Welcome to the number calculator!
    *** Version of Sun Dec 19 18:27:13 PST 2004
    > 1+2;
    expression
       'NUMBER'(1.0)
       '+'
       'NUMBER'(2.0)
    3.0
    > a+1;
    *** Undefined identifier: a
    expression
       'IDENTIFIER'(a)
       '+'
       'NUMBER'(1.0)
    > a = 3.14159;
    definition
       'IDENTIFIER'(a)
       '='
       'NUMBER'(3.14159)
    *** Defined a (3.14159)
    > b = 2*a+(a-1.234);
    definition
       'IDENTIFIER'(b)
       '='
       expression
          'NUMBER'(2.0)
          '*'
          'IDENTIFIER'(a)
          '+'
          '('
          'IDENTIFIER'(a)
          '-'
          'NUMBER'(1.234)
          ')'
    *** Defined b (8.19077)
    > a-b+2/b;
    expression
       'IDENTIFIER'(a)
       '-'
       'IDENTIFIER'(b)
       '+'
       'NUMBER'(2.0)
       '/'
       'IDENTIFIER'(b)
    -4.805002712638739
    > 1 ++ 2;
    *** Syntax Error: unexpected '+' - see stdin (line 6, column 4)
    > exit;
    *** Bye bye!...
    %

Another similar example illustrating `Jacc`'s handling of dynamic operators is described here. All concomitant files for it along with those done for the `Calculator` examples are also provided to let you run the example.

Author:
  Hassan Aït-Kaci
Copyright:
  © 2000 - present ILOG, S.A.
Version:
  Last modified on Mon Jun 09 10:58:05 2008 by hak