Using Jacc

These are instructions on how to use Jacc.

Accessing the package

Jacc is part of the ilog.language.syntax package. Its own classes use some classes in other ilog.language.* packages. This means that you must have access to all the ilog.language.* packages. To do so, all you need to do is make them accessible through your CLASSPATH environment variable by adding to it the jar file ilog_language_20061023.jar provided in the lib directory of this distribution.

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

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
Version:: Last modified on Tue Oct 24 14:03:05 2006 by hak