Parse::Eyapp::YATW(3) User Contributed Perl Documentation Parse::Eyapp::YATW(3)
NAME
Parse::Eyapp::YATW - Tree transformation objects
SYNOPSIS
#!/usr/bin/perl -w
use strict;
use Rule6;
use Parse::Eyapp::YATW;
my %BinaryOperation = (PLUS=>'+', MINUS => '-', TIMES=>'*', DIV => '/');
sub set_terminfo {
no warnings;
*TERMINAL::info = sub { $_[0]{attr} };
}
sub is_foldable {
my ($op, $left, $right);
return 0 unless defined($op = $BinaryOperation{ref($_[0])});
return 0 unless ($left = $_[0]->child(0), $left->isa('NUM'));
return 0 unless ($right = $_[0]->child(1), $right->isa('NUM'));
my $leftnum = $left->child(0)->{attr};
my $rightnum = $right->child(0)->{attr};
$left->child(0)->{attr} = eval "$leftnum $op $rightnum";
$_[0] = $left;
}
my $parser = new Rule6();
my $input = "2*3";
my $t = $parser->Run($input);
&set_terminfo;
print "
***** Before ******
";
print $t->str;
my $p = Parse::Eyapp::YATW->new(PATTERN => &is_foldable);
$p->s($t);
print "
***** After ******
";
print $t->str."
";
INTRODUCTION
"Parse::Eyapp:YATW" objects implement tree transformations. They have two attributes "PATTERN" and "NAME". "PATTERN" is a reference to
the code implementing the transformation. "NAME" is the name of the transformation.
Though usually you build a transformation by means of Treeregexp programs you can directly invoke the method "new" to build a tree
transformation. A transformation object can be built from a function that conforms to the YATW tree transformation call protocol
For a subroutine "pattern_sub" to work as a YATW tree transformation - as subroutine "is_foldable" in the SYNOPSIS section - has to
conform to the following call description:
pattern_sub(
$_[0], # Node being visited
$_[1], # Father of this node
$index, # Index of this node in @Father->children
$self, # The YATW pattern object
);
The "pattern_sub" must return TRUE if matched and FALSE otherwise.
The function "is_foldable" in the SYNOPSIS section (file "examples/YATW/foldrule6.pl") holds the properties to be a YATW tree
transformation
1 sub is_foldable {
2 my ($op, $left, $right);
3
4 return 0 unless defined($op = $BinaryOperation{ref($_[0])});
5 return 0 unless ($left = $_[0]->child(0), $left->isa('NUM'));
6 return 0 unless ($right = $_[0]->child(1), $right->isa('NUM'));
7
8 my $leftnum = $left->child(0)->{attr};
9 my $rightnum = $right->child(0)->{attr};
10 $left->child(0)->{attr} = eval "$leftnum $op $rightnum";
11 $_[0] = $left;
12 }
First, checks that the current node is one of "PLUS", "MINUS", "TIMES" or "DIV" (line 4). Then checks that both children are "NUM"bers
(lines 5 and 6). In such case proceeds to modify its left child with the result of operating both children (line 10). The matching tree is
finally substituted by its left child (line 11).
This is the output of the program in the SYNOPSIS section:
pl@nereida:~/LEyapp/examples$ eyapp Rule6.yp; foldrule6.pl
***** Before ******
TIMES(NUM(TERMINAL[2]),NUM(TERMINAL[3]))
***** After ******
NUM(TERMINAL[6])
Follows the grammar description file in "Rule6.yp":
pl@nereida:~/LEyapp/examples$ cat -n Rule6.yp
1 %{
2 use Data::Dumper;
3 %}
4 %right '='
5 %left '-' '+'
6 %left '*' '/'
7 %left NEG
8 %tree
9
10 %%
11 line: exp { $_[1] }
12 ;
13
14 exp: %name NUM
15 NUM
16 | %name VAR
17 VAR
18 | %name ASSIGN
19 VAR '=' exp
20 | %name PLUS
21 exp '+' exp
22 | %name MINUS
23 exp '-' exp
24 | %name TIMES
25 exp '*' exp
26 | %name DIV
27 exp '/' exp
28 | %name UMINUS
29 '-' exp %prec NEG
30 | '(' exp ')' { $_[2] } /* Let us simplify a bit the tree */
31 ;
32
33 %%
34
35 use Tail2;
The module "Tail2" in file "examples/Tail2.pm" implements the lexical analyzer plus the "error" and "run" methods.
Parse::Eyapp:YATW Methods
"Parse::Eyapp:YATW" objects represent tree transformations. They carry the information of what nodes match and how to modify them.
Parse::Eyapp::YATW->new
Builds a treeregexp transformation object. Though usually you build a transformation by means of Treeregexp programs you can directly
invoke the method to build a tree transformation. A transformation object can be built from a function that conforms to the YATW tree
transformation call protocol (see the section "The YATW Tree Transformation Call Protocol"). Follows an example (file
"examples/12ts_simplify_with_s.pl"):
nereida:~/src/perl/YappWithDefaultAction/examples>
sed -ne '68,$p' 12ts_simplify_with_s.pl | cat -n
1 sub is_code {
2 my $self = shift; # tree
3
4 # After the shift $_[0] is the father, $_[1] the index
5 if ((ref($self) eq 'CODE')) {
6 splice(@{$_[0]->{children}}, $_[1], 1);
7 return 1;
8 }
9 return 0;
10 }
11
12 Parse::Eyapp->new_grammar(
13 input=>$translationscheme,
14 classname=>'Calc',
15 firstline =>7,
16 );
17 my $parser = Calc->new(); # Create the parser
18
19 $parser->YYData->{INPUT} = "2*-3
"; print "2*-3
"; # Set the input
20 my $t = $parser->Run; # Parse it
21 print $t->str."
";
22 my $p = Parse::Eyapp::YATW->new(PATTERN => &is_code);
23 $p->s($t);
24 { no warnings; # make attr info available only for this display
25 local *TERMINAL::info = sub { $_[0]{attr} };
26 print $t->str."
";
27 }
After the "Parse::Eyapp::YATW" object $p is built at line 22 the call to method "$p->s($t)" applies the transformation "is_code" using a
bottom-up traversing of the tree $t. The achieved effect is the elimination of "CODE" references in the translation scheme tree. When
executed the former code produces:
nereida:~/src/perl/YappWithDefaultAction/examples> 12ts_simplify_with_s.pl
2*-3
EXP(TIMES(NUM(TERMINAL,CODE),TERMINAL,UMINUS(TERMINAL,NUM(TERMINAL,CODE),CODE),CODE),CODE)
EXP(TIMES(NUM(TERMINAL[2]),TERMINAL[*],UMINUS(TERMINAL[-],NUM(TERMINAL[3]))))
The file "foldrule6.pl" in the "examples/" distribution directory gives you another example:
nereida:~/src/perl/YappWithDefaultAction/examples> cat -n foldrule6.pl
1 #!/usr/bin/perl -w
2 use strict;
3 use Rule6;
4 use Parse::Eyapp::YATW;
5
6 my %BinaryOperation = (PLUS=>'+', MINUS => '-', TIMES=>'*', DIV => '/');
7
8 sub set_terminfo {
9 no warnings;
10 *TERMINAL::info = sub { $_[0]{attr} };
11 }
12 sub is_foldable {
13 my ($op, $left, $right);
14 return 0 unless defined($op = $BinaryOperation{ref($_[0])});
15 return 0 unless ($left = $_[0]->child(0), $left->isa('NUM'));
16 return 0 unless ($right = $_[0]->child(1), $right->isa('NUM'));
17
18 my $leftnum = $left->child(0)->{attr};
19 my $rightnum = $right->child(0)->{attr};
20 $left->child(0)->{attr} = eval "$leftnum $op $rightnum";
21 $_[0] = $left;
22 }
23
24 my $parser = new Rule6();
25 $parser->YYData->{INPUT} = "2*3";
26 my $t = $parser->Run;
27 &set_terminfo;
28 print "
***** Before ******
";
29 print $t->str;
30 my $p = Parse::Eyapp::YATW->new(PATTERN => &is_foldable);
31 $p->s($t);
32 print "
***** After ******
";
33 print $t->str."
";
when executed produces:
nereida:~/src/perl/YappWithDefaultAction/examples> foldrule6.pl
***** Before ******
TIMES(NUM(TERMINAL[2]),NUM(TERMINAL[3]))
***** After ******
NUM(TERMINAL[6])
The YATW Tree Transformation Call Protocol
For a subroutine "pattern_sub" to work as a YATW tree transformation - as subroutines "is_foldable" and "is_code" above - has to conform
to the following call description:
pattern_sub(
$_[0], # Node being visited
$_[1], # Father of this node
$index, # Index of this node in @Father->children
$self, # The YATW pattern object
);
The "pattern_sub" must return TRUE if matched and FALSE otherwise.
The protocol may change in the near future. Avoid using other information than the fact that the first argument is the node being visited.
Parse::Eyapp::YATW->buildpatterns
Works as "Parse::Eyapp->new" but receives an array of subs conforming to the YATW Tree Transformation Call Protocol.
our @all = Parse::Eyapp::YATW->buildpatt(&delete_code, &delete_tokens);
$yatw->delete
The root of the tree that is currently matched by the YATW transformation $yatw will be deleted from the tree as soon as is safe. That
usually means when the processing of their siblings is finished. The following example (taken from file
"examples/13ts_simplify_with_delete.pl" in the Parse::Eyapp distribution) illustrates how to eliminate CODE and syntactic terminals from
the syntax tree:
pl@nereida:~/src/perl/YappWithDefaultAction/examples$
sed -ne '62,$p' 13ts_simplify_with_delete.pl | cat -n
1 sub not_useful {
2 my $self = shift; # node
3 my $pat = $_[2]; # get the YATW object
4
5 (ref($self) eq 'CODE') or ((ref($self) eq 'TERMINAL') and ($self->{token} eq $self->{attr}))
6 or do { return 0 };
7 $pat->delete();
8 return 1;
9 }
10
11 Parse::Eyapp->new_grammar(
12 input=>$translationscheme,
13 classname=>'Calc',
14 firstline =>7,
15 );
16 my $parser = Calc->new(); # Create the parser
17
18 $parser->YYData->{INPUT} = "2*3
"; print $parser->YYData->{INPUT};
19 my $t = $parser->Run; # Parse it
20 print $t->str."
"; # Show the tree
21 my $p = Parse::Eyapp::YATW->new(PATTERN => ¬_useful);
22 $p->s($t); # Delete nodes
23 print $t->str."
"; # Show the tree
when executed we get the following output:
pl@nereida:~/src/perl/YappWithDefaultAction/examples$ 13ts_simplify_with_delete.pl
2*3
EXP(TIMES(NUM(TERMINAL[2],CODE),TERMINAL[*],NUM(TERMINAL[3],CODE),CODE))
EXP(TIMES(NUM(TERMINAL[2]),NUM(TERMINAL[3])))
$yatw->unshift
The call "$yatw->unshift($b)" safely unshifts (inserts at the beginning) the node $b in the list of its siblings of the node that matched
(i.e in the list of siblings of $_[0]). The following example shows a YATW transformation "insert_child" that illustrates the use of
"unshift" (file "examples/26delete_with_trreereg.pl"):
pl@nereida:~/src/perl/YappWithDefaultAction/examples$
sed -ne '70,$p' 26delete_with_trreereg.pl | cat -n
1 my $transform = Parse::Eyapp::Treeregexp->new( STRING => q{
2
3 delete_code : CODE => { $delete_code->delete() }
4
5 {
6 sub not_semantic {
7 my $self = shift;
8 return 1 if ((ref($self) eq 'TERMINAL') and ($self->{token} eq $self->{attr}));
9 return 0;
10 }
11 }
12
13 delete_tokens : TERMINAL and { not_semantic($TERMINAL) } => {
14 $delete_tokens->delete();
15 }
16
17 insert_child : TIMES(NUM(TERMINAL), NUM(TERMINAL)) => {
18 my $b = Parse::Eyapp::Node->new( 'UMINUS(TERMINAL)',
19 sub { $_[1]->{attr} = '4.5' }); # The new node will be a sibling of TIMES
20
21 $insert_child->unshift($b);
22 }
23 },
24 )->generate();
25
26 Parse::Eyapp->new_grammar(
27 input=>$translationscheme,
28 classname=>'Calc',
29 firstline =>7,
30 );
31 my $parser = Calc->new(); # Create the parser
32
33 $parser->YYData->{INPUT} = "2*3
"; print $parser->YYData->{INPUT}; # Set the input
34 my $t = $parser->Run; # Parse it
35 print $t->str."
"; # Show the tree
36 # Get the AST
37 our ($delete_tokens, $delete_code);
38 $t->s($delete_tokens, $delete_code);
39 print $t->str."
"; # Show the tree
40 our $insert_child;
41 $insert_child->s($t);
42 print $t->str."
"; # Show the tree
When is executed the program produces the following output:
pl@nereida:~/src/perl/YappWithDefaultAction/examples$ 26delete_with_trreereg.pl
2*3
EXP(TIMES(NUM(TERMINAL[2],CODE),TERMINAL[*],NUM(TERMINAL[3],CODE),CODE))
EXP(TIMES(NUM(TERMINAL[2]),NUM(TERMINAL[3])))
EXP(UMINUS(TERMINAL[4.5]),TIMES(NUM(TERMINAL[2]),NUM(TERMINAL[3])))
Don't try to take advantage that the transformation sub receives in $_[1] a reference to the father (see the section "The YATW Tree
Transformation Call Protocol") and do something like:
unshift $_[1]->{children}, $b
it is unsafe.
$yatw->insert_before
A call to "$yatw->insert_before($node)" safely inserts $node in the list of siblings of $_[0] just before $_[0] (i.e. the node that matched
with $yatw). The following example (see file "examples/YATW/moveinvariantoutofloopcomplexformula.pl") illustrates its use:
my $p = Parse::Eyapp::Treeregexp->new( STRING => q{
moveinvariant: WHILE(VAR($b), BLOCK(@a, ASSIGN($x, $e), @c))
and { is_invariant($ASSIGN, $WHILE) } => {
my $assign = $ASSIGN;
$BLOCK->delete($ASSIGN);
$moveinvariant->insert_before($assign);
}
},
);
Here the "ASSIGN($x, $e)" subtree - if is loop invariant - will be moved to the list of siblings of $WHILE just before the $WHILE. Thus a
program like
"a =1000; c = 1; while (a) { c = c*a; b = 5; a = a-1 }
"
is transformed in s.t. like:
"a =1000; c = 1; b = 5; while (a) { c = c*a; a = a-1 }
"
TREE MATCHING AND TREE SUBSTITUTION
See the documentation in Parse::Eyapp::treematchingtut
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::YATW(3)