Parse::Eyapp::Treeregexp(3)				User Contributed Perl Documentation			       Parse::Eyapp::Treeregexp(3)

NAME

       Parse::Eyapp::Treeregexp - Tree transformations

SYNOPSIS

	 use strict;
	 use Parse::Eyapp;
	 use Parse::Eyapp::Treeregexp;

	 my $grammar = q{
	   %right  '='
	   %left   '-' '+'
	   %left   '*' '/'
	   %left   NEG
	   %tree
	   %{
	   use Tail2;  # See file examples/Tail2.pm in the distribution
	   %}

	   %%
	   block:  exp <%name BLOCK + ';'> { $_[1] }
	   ;

	   exp:      %name NUM
		       NUM
		   | %name WHILE
		       'while'	 exp  '{' block '}'
		   | %name VAR
		       VAR
		   | %name ASSIGN
		       VAR '=' exp
		   | %name PLUS
		       exp '+' exp
		   | %name MINUS
		       exp '-' exp
		   | %name TIMES
		       exp '*' exp
		   | %name DIV
		       exp '/' exp
		   | %name UMINUS
		       '-' exp %prec NEG
		   |   '(' exp ')'  { $_[2] } /* Let us simplify a bit the tree */
	   ;

	   %%
	 }; # end grammar

	 sub TERMINAL::info { $_[0]{attr} }
	 $Parse::Eyapp::Node::INDENT = 2;

	 our (@all,$moveinvariant, $condition, $assign, $before, $after);

	 Parse::Eyapp->new_grammar(
	   input=>$grammar,
	   classname=>'Rule6',
	   firstline=>7,
	 );
	 my $parser = Rule6->new();
	 my $program = "a =1000; c = 1; while (a) { c = c*a; b = 5; a = a-1 }
";
	 my $t = $parser->Run($program);
	 my @output = split /
/, $t->str;

	 my $p = Parse::Eyapp::Treeregexp->new( STRING => q{
	   moveinvariant: BLOCK(
			    @prests,
			    WHILE(VAR($b), BLOCK(@a, ASSIGN($x, NUM($e)), @c)),
			    @possts
			  )
	     => {
		  my $assign = $ASSIGN;
		  $BLOCK[1]->delete($ASSIGN);
		  $BLOCK[0]->insert_before($WHILE, $assign);
		}
	   },
	 );
	 $p->generate();
	 $moveinvariant->s($t);
	 my @output2 = split /
/, $t->str;

	 my ($node1, $node2);
	 format STDOUT_TOP =
				 PROGRAM
	 -------------------------------------------------------
	 @||||||||||||||||||||||||||||||||||||||||||||||||||||||
	 $program
	 -------------------------------------------------------
	 Before 		    |	 After
	 ---------------------------|---------------------------
	 .

	 format STDOUT =
	 @<<<<<<<<<<<<<<<<<<<<<<<<<<@|@<<<<<<<<<<<<<<<<<<<<<<<<<
	 $node1,		    '|',$node2
	 .

	 for (1..$#output) {
	   $node1 = $output[$_];
	   $node2 = $output2[$_];
	   write;
	 }

Introduction
       The example in the SYNOPSIS section uses "Parse::Eyapp" to build an abstract syntax tree for the program

	 my $program = "a =1000; c = 1; while (a) { c = c*a; b = 5; a = a-1 }
";

       The tree is transformed using the transformation "moveinvariant":

	 my $p = Parse::Eyapp::Treeregexp->new( STRING => q{
	   moveinvariant: BLOCK(
			    @prests,
			    WHILE(VAR($b), BLOCK(@a, ASSIGN($x, NUM($e)), @c)),
			    @possts
			  )
	     => {
		  my $assign = $ASSIGN;
		  $BLOCK[1]->delete($ASSIGN);
		  $BLOCK[0]->insert_before($WHILE, $assign);
		}
	   },
	 );

       The output shows the original tree versus the transformed tree:

	 pl@nereida:~/LEyapp/examples$ moveinvariantoutofloopcomplexformula.pl
				 PROGRAM
	 -------------------------------------------------------

	 -------------------------------------------------------
	 Before 		    |	 After
	 ---------------------------|---------------------------
	 BLOCK( 		    | BLOCK(
	   ASSIGN(		    |	ASSIGN(
	     TERMINAL[a],	    |	  TERMINAL[a],
	     NUM(		    |	  NUM(
	       TERMINAL[1000]	    |	    TERMINAL[1000]
	     )			    |	  )
	   ) # ASSIGN,		    |	) # ASSIGN,
	   ASSIGN(		    |	ASSIGN(
	     TERMINAL[c],	    |	  TERMINAL[c],
	     NUM(		    |	  NUM(
	       TERMINAL[1]	    |	    TERMINAL[1]
	     )			    |	  )
	   ) # ASSIGN,		    |	) # ASSIGN,
	   WHILE(		    |	ASSIGN(
	     VAR(		    |	  TERMINAL[b],
	       TERMINAL[a]	    |	  NUM(
	     ), 		    |	    TERMINAL[5]
	     BLOCK(		    |	  )
	       ASSIGN(		    |	) # ASSIGN,
		 TERMINAL[c],	    |	WHILE(
		 TIMES( 	    |	  VAR(
		   VAR( 	    |	    TERMINAL[a]
		     TERMINAL[c]    |	  ),
		   ),		    |	  BLOCK(
		   VAR( 	    |	    ASSIGN(
		     TERMINAL[a]    |	      TERMINAL[c],
		   )		    |	      TIMES(
		 ) # TIMES	    |		VAR(
	       ) # ASSIGN,	    |		  TERMINAL[c]
	       ASSIGN(		    |		),
		 TERMINAL[b],	    |		VAR(
		 NUM(		    |		  TERMINAL[a]
		   TERMINAL[5]	    |		)
		 )		    |	      ) # TIMES
	       ) # ASSIGN,	    |	    ) # ASSIGN,
	       ASSIGN(		    |	    ASSIGN(
		 TERMINAL[a],	    |	      TERMINAL[a],
		 MINUS( 	    |	      MINUS(
		   VAR( 	    |		VAR(
		     TERMINAL[a]    |		  TERMINAL[a]
		   ),		    |		),
		   NUM( 	    |		NUM(
		     TERMINAL[1]    |		  TERMINAL[1]
		   )		    |		)
		 ) # MINUS	    |	      ) # MINUS
	       ) # ASSIGN	    |	    ) # ASSIGN
	     ) # BLOCK		    |	  ) # BLOCK
	   ) # WHILE		    |	) # WHILE
	 ) # BLOCK		    | ) # BLOCK

The Treeregexp Language
       A Treeregexp program is made of the repetition of three kind of primitives: The treeregexp transformations, supporting Perl code and
       Transformation Families.

	 treeregexplist:  treeregexp*

	 treeregexp:
	     IDENT ':' treereg ('=>' CODE)?  # Treeregexp
	   | CODE			     # Auxiliar code
	   | IDENT '=' IDENT + ';'	     # Transformation families

       Treeregexp themselves follow the rule:

			 IDENT ':' treereg ('=>' CODE)?

       Several instances of this rule can be seen in the example in the "SYNOPSIS" section.  The identifier "IDENT" gives the name to the rule.
       At the time of this writing (2006) there are the following kinds of treeregexes:

	 treereg:
	       /* tree patterns with children */
	     IDENT '(' childlist ')' ('and' CODE)?
	   | REGEXP (':' IDENT)? '(' childlist ')' ('and' CODE)?
	   | SCALAR '(' childlist ')' ('and' CODE)?
	   | '.' '(' childlist ')' ('and' CODE)?
		 /* leaf tree patterns */
	   | IDENT ('and' CODE)?
	   | REGEXP (':' IDENT)? ('and' CODE)?
	   | '.' ('and' CODE)?
	   | SCALAR ('and' CODE)?
	   | ARRAY
	   | '*'

   Treeregexp rules
       When seen a rule like

	   zero_times: TIMES(NUM($x), ., .) and { $x->{attr} == 0 } => { $_[0] = $NUM }

       The Treeregexp translator creates a "Parse::Eyapp:YATW" object that can be later referenced in the user code by the package variable
       $zero_times.

       The treeregexp

       The first part of the rule "TIMES(NUM($x), ., .)"  indicates that for a matching to succeed the node being visited must be of "type"
       "TIMES", have a left child of  "type" "NUM" and two more children.

       If the first part succeeded then the following part takes the control to see if the semantic conditions are satisfied.

       Semantic condition

       The second part is optional and must be prefixed by the reserved word "and" followed by a Perl code manifesting the semantic conditions
       that must be hold by the node to succeed. Thus, in the example:

	 zero_times: TIMES(NUM($x), ., .) and { $x->{attr} == 0 } => { $_[0] = $NUM }

       the semantic condition "$x->{attr} == 0" states that the value of the number stored in the "TERMINAL" node referenced by $x must be zero.

       Referencing the matching nodes

       The node  being visited can be referenced/modified inside the semantic actions using $_[0].

       The Treeregexp translator automatically creates a set of lexical variables for us. The scope of these variables is limited to the semantic
       condition and the transformation code.

       Thus, in the example

	 zero_times: TIMES(NUM($x), ., .) and { $x->{attr} == 0 } => { $_[0] = $NUM }

       the node being visited $_[0] can be also referenced using the lexical variable $TIMES which is created by he Treeregexp compiler.  In the
       same way a reference to the left child "NUM" will be stored in the lexical variable $NUM and a reference to the child of $NUM will be
       stored in $x.  The semantic condition states that the attribute of the node associated with $x must be zero.

       When the same type of node appears several times inside the treeregexp part the associated lexical variable is declared by the Treeregexp
       compiler as an array.  This is the case in the "constantfold" transformation in the "SYNOPSIS" example, where there are two nodes of type
       "NUM":

	 constantfold: /TIMES|PLUS|DIV|MINUS/(NUM($x), ., NUM($y))
	    => {
	   $x->{attr} = eval  "$x->{attr} $W->{attr} $y->{attr}";
	   $_[0] = $NUM[0];
	 }

       Thus variable  $NUM[0] references the node that matches the first "NUM" term in the formula and $NUM[1] the one that matches the second.

       Transformation code

       The third part of the rule is also optional and comes prefixed by the big arrow "=>". The Perl code in this section usually transforms the
       matching tree.  To achieve the modification of the tree, the Treeregexp programmer must use $_[0] and not the lexical variables provided by
       the translator.	Remember that in Perl $_[0] is an alias of the actual parameter.  The "constantfold" example above will not work if we
       rewrite the code $_[0] = $NUM[0] as

				   { $TIMES = $NUM }

   Regexp Treeregexes
       The previous "constantfold" example used a classic Perl linear regexp to explicit that the root node of the matching subtree must match the
       Perl regexp.  The general syntax for "REGEXP" treeregexes patterns is:

	     treereg: REGEXP (':' IDENT)? '(' childlist ')' ('and' CODE)?

       The "REGEXP" must be specified between slashes (other delimiters as "{}" are not accepted).  It is legal to specify options after the
       second slash (like "e", "i", etc.).

       The operation of string oriented regexps is slightly modified when they are used inside a treeregexp: by default the option "x" will be
       assumed.  The treeregexp compiler will automatically insert it.	Use the new option "X" (upper case X) if you want to suppress such
       behavior.  There is no need also to insert "" word anchors to delimit identifiers: all the identifiers in a regexp treeregexp are
       automatically surrounded by "". Use the option "B" (upper case B) to suppress this behavior.

       The optional identifier after the "REGEXP" indicates the name of the lexical variable that will be held a reference to the node whose type
       matches "REGEXP".  Variable $W (or @W if there are more than one REGEXP and or dot treeregexes) will be used instead if no identifier is
       specified.

   Scalar Treeregexes
       A scalar treeregxp is defined writing a Perl scalar inside the treeregexp, like $x in "NUM($x)". A scalar treeregxp immediately matches any
       node that exists and stores a reference to such node inside the Perl lexical scalar variable.  The scope of the variable is limited to the
       semantic parts of the Treeregexp.  Is illegal to use $W or "$W_#num" as variable names for scalar treeregexes.

   Dot Treeregexes
       A dot matches any node. It can be seen as an abbreviation for scalar treeregexes. The reference to the matching node is stored in the
       lexical variable $W.  The variable @W will be used instead if there are more than one REGEXP and or dot treeregexes

   Array Treeregexp Expressions
       The Treeregexp language permits expressions like:

			  A(@a,B($x),@c)

       After the matching variable @A contains the shortest prefix of "$A->children" that does not match "B($x)".  The variable @c contains the
       remaining suffix of
	"$A->children".

       The following example uses array treereg expressions to move the assignment "b = 5" out of the "while" loop:

	 ..  ......................................................................
	 93  my $program = "a =1000; c = 1; while (a) { c = c*a; b = 5; a = a-1 }
";
	 94  $parser->YYData->{INPUT} = $program;
	 95  my $t = $parser->Run;
	 96  my @output = split /
/, $t->str;
	 97
	 98  my $p = Parse::Eyapp::Treeregexp->new( STRING => q{
	 99    moveinvariant: BLOCK(
	100			@prests,
	101			WHILE(VAR($b), BLOCK(@a, ASSIGN($x, NUM($e)), @c)),
	102			@possts
	103		      )
	104	 => {
	105	      my $assign = $ASSIGN;
	106	      $BLOCK[1]->delete($ASSIGN);
	107	      $BLOCK[0]->insert_before($WHILE, $assign);
	108	    }
	109    },
	110    FIRSTLINE => 99,
	111  );
	112  $p->generate();

   Star Treeregexp
       Deprecated. Don't use it. Is still there but not to endure.

   Transformation Families
       Transformations created by "Parse::Eyapp::Treeregexp" can be grouped in families. That is the function of the rule:

			   treeregexp: IDENT '=' IDENT + ';'

       The next example (file "examples/TSwithtreetransformations3.eyp") defines the family

	    algebraic_transformations = constantfold zero_times times_zero comasocfold;

       Follows the code:

	    my $transform = Parse::Eyapp::Treeregexp->new( STRING => q{

	     uminus: UMINUS(., NUM($x), .) => { $x->{attr} = -$x->{attr}; $_[0] = $NUM }
	     constantfold: /TIMES|PLUS|DIV|MINUS/:bin(NUM($z), ., NUM($y))
		=> {
	       $z->{attr} = eval  "$z->{attr} $W->{attr} $y->{attr}";
	       $_[0] = $NUM[0];
	     }
	     commutative_add: PLUS($x, ., $y, .)
	       => { my $t = $x; $_[0]->child(0, $y); $_[0]->child(2, $t)}
	     comasocfold: TIMES(DIV(NUM($x), ., $b), ., NUM($y))
		=> {
	       $x->{attr} = $x->{attr} * $y->{attr};
	       $_[0] = $DIV;
	     }
	     zero_times: TIMES(NUM($x), ., .) and { $x->{attr} == 0 } => { $_[0] = $NUM }
	     times_zero: TIMES(., ., NUM($x)) and { $x->{attr} == 0 } => { $_[0] = $NUM }
	     algebraic_transformations = constantfold zero_times times_zero comasocfold;
	   },
	   );

	   $transform->generate();
	   our ($uminus);
	   $uminus->s($tree);

       The transformations belonging to a family are usually applied together:

		       $tree->s(@algebraic_transformations);

   Code Support
       In between Treeregexp rules and family assignments the programmer can insert Perl code between curly brackets. That code usually gives
       support to the semantic conditions and transformations inside the rules.  See for example test 14 in the "t/" directory of the Parse::Eyapp
       distribution.

	 {
	   sub not_semantic {
	     my $self = shift;
	     return  1 if $self->{token} eq $self->{attr};
	     return 0;
	   }
	 }

	 delete_tokens : TERMINAL and { not_semantic($TERMINAL) }
				  => { $delete_tokens->delete() }

SEE ALSO

       o   The project home is at http://code.google.com/p/parse-eyapp/ <http://code.google.com/p/parse-eyapp/>.  Use a subversion client to
	   anonymously check out the latest project source code:

	      svn checkout http://parse-eyapp.googlecode.com/svn/trunk/ parse-eyapp-read-only

       o   The tutorial Parsing Strings and Trees with "Parse::Eyapp" (An Introduction to Compiler Construction in seven pages) in
	   <http://nereida.deioc.ull.es/~pl/eyapsimple/>

       o   Parse::Eyapp, Parse::Eyapp::eyapplanguageref, Parse::Eyapp::debuggingtut, Parse::Eyapp::defaultactionsintro,
	   Parse::Eyapp::translationschemestut, Parse::Eyapp::Driver, Parse::Eyapp::Node, Parse::Eyapp::YATW, Parse::Eyapp::Treeregexp,
	   Parse::Eyapp::Scope, Parse::Eyapp::Base, Parse::Eyapp::datagenerationtut

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

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

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

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

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

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

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

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

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

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

       o   perldoc eyapp,

       o   perldoc treereg,

       o   perldoc vgg,

       o   The Syntax Highlight file for vim at <http://www.vim.org/scripts/script.php?script_id=2453> and <http://nereida.deioc.ull.es/~vim/>

       o   Analisis Lexico y Sintactico, (Notes for a course in compiler construction) by  Casiano Rodriguez-Leon.  Available at
	   <http://nereida.deioc.ull.es/~pl/perlexamples/> Is the more complete and reliable source for Parse::Eyapp. However is in Spanish.

       o   Parse::Yapp,

       o   Man pages of yacc(1) and bison(1), <http://www.delorie.com/gnu/docs/bison/bison.html>

       o   Language::AttributeGrammar

       o   Parse::RecDescent.

       o   HOP::Parser

       o   HOP::Lexer

       o   ocamlyacc tutorial at http://plus.kaist.ac.kr/~shoh/ocaml/ocamllex-ocamlyacc/ocamlyacc-tutorial/ocamlyacc-tutorial.html
	   <http://plus.kaist.ac.kr/~shoh/ocaml/ocamllex-ocamlyacc/ocamlyacc-tutorial/ocamlyacc-tutorial.html>

REFERENCES

       o   The classic Dragon's book Compilers: Principles, Techniques, and Tools by Alfred V. Aho, Ravi Sethi and Jeffrey D. Ullman (Addison-
	   Wesley 1986)

       o   CS2121: The Implementation and Power of Programming Languages (See <http://www.cs.man.ac.uk/~pjj>,
	   <http://www.cs.man.ac.uk/~pjj/complang/g2lr.html> and <http://www.cs.man.ac.uk/~pjj/cs2121/ho/ho.html>) by Pete Jinks

CONTRIBUTORS

       o Hal Finkel <http://www.halssoftware.com/>

       o G. Williams <http://kasei.us/>

       o Thomas L. Shinnick <http://search.cpan.org/~tshinnic/>

       o Frank Leray

AUTHOR

       Casiano Rodriguez-Leon (casiano@ull.es)

ACKNOWLEDGMENTS

       This work has been supported by CEE (FEDER) and the Spanish Ministry of Educacion y Ciencia through Plan Nacional I+D+I number
       TIN2005-08818-C04-04 (ULL::OPLINK project <http://www.oplink.ull.es/>).	Support from Gobierno de Canarias was through GC02210601 (Grupos
       Consolidados).  The University of La Laguna has also supported my work in many ways and for many years.

       A large percentage of  code is verbatim taken from Parse::Yapp 1.05.  The author of Parse::Yapp is Francois Desarmenien.

       I wish to thank Francois Desarmenien for his Parse::Yapp module, to my students at La Laguna and to the Perl Community. Thanks to the
       people who have contributed to improve the module (see "CONTRIBUTORS" in Parse::Eyapp).	Thanks to Larry Wall for giving us Perl.  Special
       thanks to Juana.

LICENCE AND COPYRIGHT

       Copyright (c) 2006-2008 Casiano Rodriguez-Leon (casiano@ull.es). All rights reserved.

       Parse::Yapp copyright is of Francois Desarmenien, all rights reserved. 1998-2001

       These modules are free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

perl v5.16.2							    2012-03-23					       Parse::Eyapp::Treeregexp(3)