NAME

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

SYNOPSIS

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

DESCRIPTION

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.

OPTIONS IN DETAIL

-v

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.

-s

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;

-n

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 grammar.pm or, if you specified the option -m A::Module::Name (see below), to Name.pm.

-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 Parse::Eyapp::Output.pm. For how to write your own template and which substitutions are available, have a look to the module Parse::Eyapp::Output.pm : 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.pl myscript.yp

This will output a file called myscript.pl 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.

-l

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

grammar

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.

-V

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

-h

Display the usage screen.

EXAMPLE

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 postfix.pl -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$ ./postfix.pl -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$ ./postfix.pl -c 'a = 2**3 +b'

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

AUTHOR

Casiano Rodriguez-Leon

COPYRIGHT

Copyright © 2006, 2007, 2008, 2009, 2010, 2011, 2012 Casiano Rodriguez-Leon. Copyright © 2017 William N. Braswell, Jr. All Rights Reserved.

Parse::Yapp is Copyright © 1998, 1999, 2000, 2001, Francois Desarmenien. Parse::Yapp is Copyright © 2017 William N. Braswell, Jr. All Rights Reserved.

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.

SEE ALSO

• Parse::Eyapp,

• perldoc vgg,

• The tutorial Parsing Strings and Trees with Parse::Eyapp (An Introduction to Compiler Construction in seven pages)> in

• The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/Eyapp.pdf

• http://nereida.deioc.ull.es/~pl/perlexamples/section_eyappts.html (Spanish),

• eyapp,

• treereg,

• Parse::yapp,

• yacc(1),

• bison(1),

• the classic book "Compilers: Principles, Techniques, and Tools" by Alfred V. Aho, Ravi Sethi and

• Jeffrey D. Ullman (Addison-Wesley 1986)

• Parse::RecDescent.