EYAPP(1)						User Contributed Perl Documentation						  EYAPP(1)

NAME

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

SYNOPSYS

	   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
" }
	   ;

	   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

       (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.

SEE ALSO

       o   Parse::Eyapp,

       o   perldoc vgg,

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

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

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

       o   eyapp,

       o   treereg,

       o   Parse::yapp,

       o   yacc(1),

       o   bison(1),

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

       o   Jeffrey D. Ullman (Addison-Wesley 1986)

       o   Parse::RecDescent.

perl v5.12.5							    2011-01-30								  EYAPP(1)