Casiano Rodriguez-Leon > Parse-Eyapp > eyapp


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eyapp - A Perl front-end to the Parse::Eyapp module


    eyapp [options] grammar[.eyp]
    eyapp -V
    eyapp -h

        grammar     The grammar file. If no suffix is given, and the file
                    does not exists, .eyp is added


The eyapp compiler is a front-end to the Parse::Eyapp module, which lets you compile Parse::Eyapp grammar input files into Perl LALR(1) Object Oriented parser modules.



Creates a file grammar.output describing your parser. It will show you a summary of conflicts, rules, the DFA (Deterministic Finite Automaton) states and overall usage of the parser.

Implies option -N. To produce a more detailed description of the states, the LALR tables aren't compacted. Use the combination -vN to produce an .output file corresponding to the compacted tables.


Create a standalone module in which the parsing driver is included. The modules including the LALR driver (Parse::Eyapp::Driver), those for AST manipulations (Parse::Eyapp::Node and Parse::Eyapp::YATW)) and Parse::Eyapp::Base are included - almost verbatim - inside the generated module.

Note that if you have more than one parser module called from a program, to have it standalone, you need this option only for one of your grammars;


Disable source file line numbering embedded in your parser module. I don't know why one should need it, but it's there.

-m module

Gives your parser module the package name (or name space or module name or class name or whatever-you-call-it) of module. It defaults to grammar

-o outfile

The compiled output file will be named outfile for your parser module. It defaults to or, if you specified the option -m A::Module::Name (see below), to

-c grammar[.eyp]

Produces as output (STDOUT) the grammar without the actions. Only the syntactic parts are displayed. Comments will be also stripped if the -v option is added.

-t filename

The -t filename option allows you to specify a file which should be used as template for generating the parser output. The default is to use the internal template defined in For how to write your own template and which substitutions are available, have a look to the module : it should be obvious.

-b shebang

If you work on systems that understand so called shebangs, and your generated parser is directly an executable script, you can specify one with the -b option, ie:

    eyapp -b '/usr/local/bin/perl -w' -o myscript.yp

This will output a file called whose very first line is:

    #!/usr/local/bin/perl -w

The argument is mandatory, but if you specify an empty string, the value of $Config{perlpath} will be used instead.

-B prompt

Adds a modulino call '__PACKAGE->main(<prompt>) unless caller();' as the very last line of the output file. The argument is mandatory.

-C grammar.eyp

An abbreviation for the combined use of -b '' and -B ''

-T grammar.eyp

Equivalent to %tree.

-N grammar.eyp

Equivalent to the directive %nocompact. Do not compact LALR action tables.


Do not provide a default lexical analyzer. By default eyapp builds a lexical analyzer from your %token = /regexp/ definitions


The input grammar file. If no suffix is given, and the file does not exists, an attempt to open the file with a suffix of .eyp is tried before exiting.


Display current version of Parse::Eyapp and gracefully exits.


Display the usage screen.


The following eyapp program translates an infix expression like 2+3*4 to postfix: 2 3 4 * +

    %token NUM = /([0-9]+(?:\.[0-9]+)?)/
    %token VAR = /([A-Za-z][A-Za-z0-9_]*)/

    %right  '='
    %left   '-' '+'
    %left   '*' '/'
    %left   NEG

    %defaultaction { "$left $right $op"; }

    line: $exp  { print "$exp\n" }

    exp:        $NUM  { $NUM }            
            |   $VAR  { $VAR }            
            |   VAR.left '='.op exp.right         
            |   exp.left '+'.op exp.right         
            |   exp.left '-'.op exp.right        
            |   exp.left '*'.op exp.right       
            |   exp.left '/'.op exp.right      
            |   '-' $exp %prec NEG { "$exp NEG" }
            |   '(' $exp ')' { $exp }      


Notice that there is no need to write lexer and error report subroutines. First, we compile the grammar:

    pl@nereida:~/LEyapp/examples/eyappintro$ eyapp -o -C Postfix.eyp 

If we use the -C option and no main() was written one default main sub is provided. We can now execute the resulting program:

    pl@nereida:~/LEyapp/examples/eyappintro$ ./ -c 'a = 2*3 +b'
    a 2 3 * b + =

When a non conformant input is given, it produces an accurate error message:

    pl@nereida:~/LEyapp/examples/eyappintro$ ./ -c 'a = 2**3 +b'

    Syntax error near '*'. 
    Expected one of these terminals: '-' 'NUM' 'VAR' '('
    There were 1 errors during parsing


Casiano Rodriguez-Leon


(c) Copyright 2006 Casiano Rodriguez-Leon

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.


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