NAME
Parse::Eyapp::Node - The nodes of the Syntax Trees
SYNOPSIS
use Parse::Eyapp;
use Parse::Eyapp::Treeregexp;
sub TERMINAL::info {
$_[0]{attr}
}
my $grammar = q{
%right '=' # Lowest precedence
%left '-' '+' # + and - have more precedence than = Disambiguate a-b-c as (a-b)-c
%left '*' '/' # * and / have more precedence than + Disambiguate a/b/c as (a/b)/c
%left NEG # Disambiguate -a-b as (-a)-b and not as -(a-b)
%tree # Let us build an abstract syntax tree ...
%%
line:
exp <%name EXPRESSION_LIST + ';'>
{ $_[1] } /* list of expressions separated by ';' */
;
/* The %name directive defines the name of the class to which the node being built belongs */
exp:
%name NUM
NUM
| %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 ')'
{ $_[2] } /* Let us simplify a bit the tree */
;
%%
sub _Error { die "Syntax error near ".($_[0]->YYCurval?$_[0]->YYCurval:"end of file")."\n" }
sub _Lexer {
my($parser)=shift; # The parser object
for ($parser->YYData->{INPUT}) { # Topicalize
m{\G\s+}gc;
$_ eq '' and return('',undef);
m{\G([0-9]+(?:\.[0-9]+)?)}gc and return('NUM',$1);
m{\G([A-Za-z][A-Za-z0-9_]*)}gc and return('VAR',$1);
m{\G(.)}gcs and return($1,$1);
}
return('',undef);
}
sub Run {
my($self)=shift;
$self->YYParse( yylex => \&_Lexer, yyerror => \&_Error, );
}
}; # end grammar
our (@all, $uminus);
Parse::Eyapp->new_grammar( # Create the parser package/class
input=>$grammar,
classname=>'Calc', # The name of the package containing the parser
firstline=>7 # String $grammar starts at line 7 (for error diagnostics)
);
my $parser = Calc->new(); # Create a parser
$parser->YYData->{INPUT} = "2*-3+b*0;--2\n"; # Set the input
my $t = $parser->Run; # Parse it!
local $Parse::Eyapp::Node::INDENT=2;
print "Syntax Tree:",$t->str;
# Let us transform the tree. Define the tree-regular expressions ..
my $p = Parse::Eyapp::Treeregexp->new( STRING => q{
{ # Example of support code
my %Op = (PLUS=>'+', MINUS => '-', TIMES=>'*', DIV => '/');
}
constantfold: /TIMES|PLUS|DIV|MINUS/:bin(NUM($x), NUM($y))
=> {
my $op = $Op{ref($bin)};
$x->{attr} = eval "$x->{attr} $op $y->{attr}";
$_[0] = $NUM[0];
}
uminus: UMINUS(NUM($x)) => { $x->{attr} = -$x->{attr}; $_[0] = $NUM }
zero_times_whatever: TIMES(NUM($x), .) and { $x->{attr} == 0 } => { $_[0] = $NUM }
whatever_times_zero: TIMES(., NUM($x)) and { $x->{attr} == 0 } => { $_[0] = $NUM }
},
OUTPUTFILE=> 'main.pm'
);
$p->generate(); # Create the tranformations
$t->s($uminus); # Transform UMINUS nodes
$t->s(@all); # constant folding and mult. by zero
local $Parse::Eyapp::Node::INDENT=0;
print "\nSyntax Tree after transformations:\n",$t->str,"\n";
METHODS
The Parse::Eyapp::Node
objects represent the nodes of the syntax tree. All the node classes build by %tree
and %metatree
directives inherit from Parse::Eyapp::Node
and consequently have acces to the methods provided in such module.
The examples used in this document can be found in the directory examples/Node
accompanying the distribution of Parse::Eyapp.
Parse::Eyapp::Node->new
Nodes are usually created from a Eyapp grammar using the %tree
or %metatree
directives. The Parse::Eyapp::Node
constructor new
offers an alternative way to create forests.
This class method can be used to build multiple nodes on a row. It receives a string describing the tree and optionally a reference to a subroutine. Such subroutine (called the attribute handler) is in charge to initialize the attributes of the just created nodes. The attribute handler is called with the array of references to the nodes as they appear in the string from left to right.
Parse::Eyapp::Node->new
returns an array of pointers to the nodes created as they appear in the input string from left to right. In scalar context returns a pointer to the first of these trees.
The following example (see file examples/Node/28foldwithnewwithvars.pl
) of a treeregexp transformation creates a new NUM(TERMINAL)
node using Parse::Eyapp::Node->new
:
my $p = Parse::Eyapp::Treeregexp->new( STRING => q{
{
my %Op = (PLUS=>'+', MINUS => '-', TIMES=>'*', DIV => '/');
}
constantfold: /TIMES|PLUS|MINUS|DIV/(NUM($x), NUM($y))
=> {
my $op = $Op{ref($_[0])};
my $res = Parse::Eyapp::Node->new(
q{NUM(TERMINAL)},
sub {
my ($NUM, $TERMINAL) = @_;
$TERMINAL->{attr} = eval "$x->{attr} $op $y->{attr}";
$TERMINAL->{token} = 'NUM';
},
);
$_[0] = $res;
}
},
);
The call to Parse::Eyapp::Node->new
creates a tree NUM(TERMINAL)
and decorates the TERMINAL
leaf with attributes attr
and token
. The constantfold
transformation substitutes all the binary operation trees whose children are numbers for a NUM(TERMINAL)
tree holding as attribute the number resulting of operating the two numbers.
The input string can describe more than one tree. Different trees are separated by white spaces. Consider the following example (in examples/Node/builder.pl
):
$ cat -n builder.pl
1 #!/usr/bin/perl -w
2 use strict;
3 use Parse::Eyapp::Node;
4
5 use Data::Dumper;
6 $Data::Dumper::Indent = 1;
7 $Data::Dumper::Purity = 1;
8
9 my $string = shift || 'ASSIGN(VAR(TERMINAL), TIMES(NUM(TERMINAL),NUM(TERMINAL))) ';
10 my @t = Parse::Eyapp::Node->new(
11 $string,
12 sub { my $i = 0; $_->{n} = $i++ for @_ }
13 );
14
15 print "****************\n";
16 print Dumper(\@t);
When feed with input 'A(C,D) E(F)'
the following forest is built:
$ builder.pl 'A(C,D) E(F)'
****************
$VAR1 = [
bless( {
'n' => 0,
'children' => [
bless( { 'n' => 1, 'children' => [] }, 'C' ),
bless( { 'n' => 2, 'children' => [] }, 'D' )
]
}, 'A' ),
{},
{},
bless( {
'n' => 3,
'children' => [
bless( { 'n' => 4, 'children' => [] }, 'F' )
]
}, 'E' ),
{}
];
$VAR1->[1] = $VAR1->[0]{'children'}[0];
$VAR1->[2] = $VAR1->[0]{'children'}[1];
$VAR1->[4] = $VAR1->[3]{'children'}[0];
Thusm, the forest @t
contains 5 subtrees A(C,D), C, D, E(F)
and F
.
Directed Acyclic Graphs with Parse::Eyapp::Node->hnew
Parse::Eyapp
provides the method Parse::Eyapp::Node->hnew
to build Directed Acyclic Graphs (DAGs) instead of trees. They are built using hashed consing, i.e. memoizing the creation of nodes.
The method Parse::Eyapp::Node->hnew
works very much like Parse::Eyapp::Node->new
but if one of the implied trees was previously built, hnew
returns a reference to the existing one.
See the following debugger session where several DAGs describing type expressions are built:
DB<2> x $a = Parse::Eyapp::Node->hnew('F(X_3(A_3(A_5(INT)), CHAR, A_5(INT)),CHAR)')
0 F=HASH(0x85f6a20)
'children' => ARRAY(0x85e92e4)
|- 0 X_3=HASH(0x83f55fc)
| 'children' => ARRAY(0x83f5608)
| |- 0 A_3=HASH(0x85a0488)
| | 'children' => ARRAY(0x859fad4)
| | 0 A_5=HASH(0x85e5d3c)
| | 'children' => ARRAY(0x83f4120)
| | 0 INT=HASH(0x83f5200)
| | 'children' => ARRAY(0x852ccb4)
| | empty array
| |- 1 CHAR=HASH(0x8513564)
| | 'children' => ARRAY(0x852cad4)
| | empty array
| `- 2 A_5=HASH(0x85e5d3c)
| -> REUSED_ADDRESS
`- 1 CHAR=HASH(0x8513564)
-> REUSED_ADDRESS
DB<3> x $a->str
0 'F(X_3(A_3(A_5(INT)),CHAR,A_5(INT)),CHAR)'
The second occurrence of A_5(INT)
is labelled REUSED_ADDRESS
. The same occurs with the second instance of CHAR
.
Parse::Eyapp::Node->hnew
can be more convenient than new
in some compiler phases and tasks like detecting common subexpressions or during type checking. See file Types.eyp
in examples/typechecking/Simple-Types-XXX.tar.gz
for a more comprehensive example.
Expanding Directed Acyclic Graphs with Parse::Eyapp::Node->hexpand
Calls to Parse::Eyapp::Node->hexpand
have the syntax
$z = Parse::Eyapp::Node->hexpand('CLASS', @children, \&handler)
Creates a dag of type 'CLASS'
with children @children
in a way compatible with hnew
. The last optional argument can be a reference to a sub. Such sub will be called after the creation of the DAG with a reference to the root of the DAG as single argument. The following session with the debugger illustrates the use of Parse::Eyapp::Node->hexpand
. First we create a DAG using hnew
:
pl@nereida:~/Lbook/code/Simple-Types/script$ perl -MParse::Eyapp::Node -wde 0
main::(-e:1): 0
DB<1> $x = Parse::Eyapp::Node->hnew('A(C(B),C(B))')
DB<2> x $x
0 A=HASH(0x850c850)
'children' => ARRAY(0x850ca30)
0 C=HASH(0x850c928)
'children' => ARRAY(0x850c9e8)
0 B=HASH(0x850c9a0)
'children' => ARRAY(0x83268c8)
empty array
1 C=HASH(0x850c928)
-> REUSED_ADDRESS
We obtain the REUSED_ADDRESS
for the second child since the C(B)
subtree appears twice. Now, suppose we want to expand the exsting tree/DAG C(B)
to A(C(B))
. We can do that using hexpand
:
DB<3> $y = Parse::Eyapp::Node->hexpand('A', $x->child(0))
DB<4> x $y
0 A=HASH(0x8592558)
'children' => ARRAY(0x832613c)
0 C=HASH(0x850c928)
'children' => ARRAY(0x850c9e8)
0 B=HASH(0x850c9a0)
'children' => ARRAY(0x83268c8)
empty array
We get new memory for C<$y>: C<HASH(0x8592558)> is anew address.
Assume we want to expand the tree/DAG C<C(B)> to C<A(C(B),C(B))>.
We can do it this way:
DB<5> $z = Parse::Eyapp::Node->hexpand('A', $x->children)
DB<6> x $z
0 A=HASH(0x850c850)
'children' => ARRAY(0x850ca30)
0 C=HASH(0x850c928)
'children' => ARRAY(0x850c9e8)
0 B=HASH(0x850c9a0)
'children' => ARRAY(0x83268c8)
empty array
1 C=HASH(0x850c928)
-> REUSED_ADDRESS
Notice that the address c<0x850c850> for $z
is the same than the address for $x
. No new memory has been allocated for $z
.
The following command illustrates the use of hexpand
with a handler:
DB<7> $z = Parse::Eyapp::Node->hexpand('A', $x->children, sub { $_[0]->{t} = "X" })
DB<8> x $z
0 A=HASH(0x850c850)
'children' => ARRAY(0x850ca30)
0 C=HASH(0x850c928)
'children' => ARRAY(0x850c9e8)
0 B=HASH(0x850c9a0)
'children' => ARRAY(0x83268c8)
empty array
1 C=HASH(0x850c928)
-> REUSED_ADDRESS
't' => 'X'
$node->type
Returns (or sets) the type (class) of the node. It can be called as a subroutine when $node
is not a Parse::Eyapp::Node
like this:
Parse::Eyapp::Node::type($scalar)
This is the case when visiting CODE
nodes.
The following session with the debugger illustrates how it works:
> perl -MParse::Eyapp::Node -de0
DB<1> @t = Parse::Eyapp::Node->new("A(B,C)") # Creates a tree
DB<2> x map { $_->type } @t # Get the types of the three nodes
0 'A'
1 'B'
2 'C'
DB<3> x Parse::Eyapp::Node::type(sub {})
0 'CODE'
DB<4> x Parse::Eyapp::Node::type("hola")
0 'Parse::Eyapp::Node::STRING'
DB<5> x Parse::Eyapp::Node::type({ a=> 1})
0 'HASH'
DB<6> x Parse::Eyapp::Node::type([ a, 1 ])
0 'ARRAY'
As it is shown in the example it can be called as a subroutine with a (CODE/HASH/ARRAY) reference or an ordinary scalar.
The words HASH, CODE, ARRAY and STRING are reserved for ordinary Perl references. Avoid naming a AST node with one of those words.
To be used as a setter, be sure Parse::Eyapp::Driver is loaded:
$ perl -MParse::Eyapp::Driver -MParse::Eyapp::Node -wde0
main::(-e:1): 0
DB<1> x $t = Parse::Eyapp::Node->new("A(B,C)") # Creates a tree
0 A=HASH(0x8557bdc)
'children' => ARRAY(0x8557c90)
0 B=HASH(0x8557cf0)
'children' => ARRAY(0x8325804)
empty array
1 C=HASH(0x8557c6c)
'children' => ARRAY(0x8557d5c)
empty array
DB<2> x $t->type('FUN') # Change the type of $t to 'FUN'
0 'FUN'
DB<3> x $t
0 FUN=HASH(0x8557bdc)
'children' => ARRAY(0x8557c90)
0 B=HASH(0x8557cf0)
'children' => ARRAY(0x8325804)
empty array
1 C=HASH(0x8557c6c)
'children' => ARRAY(0x8557d5c)
empty array
DB<4> x $t->isa('Parse::Eyapp::Node')
0 1
$node->child
Setter-getter to modify a specific child of a node. It is called like:
$node->child($i)
Returns the child with index $i. Returns undef
if the child does not exists. It has two obligatory parameters: the node (since it is a method) and the index of the child. Sets the new value if called
$node->child($i, $tree)
The method will croak if the obligatory parameters are not provided.
In the files examples/Node/TSwithtreetransformations2.eyp
and examples/node/usetswithtreetransformations2.pl
) you can find a somewhat complicated example of call to child
as a setter. It is inside a transformation that swaps the children of a PLUS
node (remember that the tree is a concrete tree including code since it is a translation scheme built under the directive %metatree
):
my $transform = Parse::Eyapp::Treeregexp->new( STRING => q{
........................................................
commutative_add: PLUS($x, ., $y, .) # 1st dot correspond to '+' 2nd dot to CODE
=> { my $t = $x; $_[0]->child(0, $y); $_[0]->child(2, $t)}
........................................................
}
Child Access Through %tree alias
Remember that when the Eyapp
program runs under the %tree alias
directive The dot and dollar notations can be used to generate named getter-setters to access the children:
examples/Node$ cat -n alias_and_yyprefix.pl
1 #!/usr/local/bin/perl
2 use warnings;
3 use strict;
4 use Parse::Eyapp;
5
6 my $grammar = q{
7 %prefix R::S::
8
9 %right '='
10 %left '-' '+'
11 %left '*' '/'
12 %left NEG
13 %tree bypass alias
14
15 %%
16 line: $exp { $_[1] }
17 ;
18
19 exp:
20 %name NUM
21 $NUM
22 | %name VAR
23 $VAR
24 | %name ASSIGN
25 $VAR '=' $exp
26 | %name PLUS
27 exp.left '+' exp.right
28 | %name MINUS
29 exp.left '-' exp.right
30 | %name TIMES
31 exp.left '*' exp.right
32 | %name DIV
33 exp.left '/' exp.right
34 | %no bypass UMINUS
35 '-' $exp %prec NEG
36 | '(' exp ')' { $_[2] } /* Let us simplify a bit the tree */
37 ;
38
39 %%
40
.............................
76 }; # end grammar
77
78
79 Parse::Eyapp->new_grammar(
80 input=>$grammar,
81 classname=>'Alias',
82 firstline =>7,
83 outputfile => 'main',
84 );
85 my $parser = Alias->new();
86 $parser->YYData->{INPUT} = "a = -(2*3+5-1)\n";
87 my $t = $parser->Run;
88 $Parse::Eyapp::Node::INDENT=0;
89 print $t->VAR->str."\n"; # a
90 print "***************\n";
91 print $t->exp->exp->left->str."\n"; # 2*3+5
92 print "***************\n";
93 print $t->exp->exp->right->str."\n"; # 1
Here methods with names left
and right
will be created inside the class R::S
(see the use of the %prefix
directive in line 7) to access the corresponding children associated with the two instances of exp
in the right hand side of the production rule. when executed, teh former program produces this output:
examples/Node$ alias_and_yyprefix.pl
R::S::TERMINAL
***************
R::S::PLUS(R::S::TIMES(R::S::NUM,R::S::NUM),R::S::NUM)
***************
R::S::NUM
$node->children
Returns the array of children of the node. When the tree is a translation scheme the CODE references are also included. See examples/Node/TSPostfix3.eyp
for an example of use inside a Translation Scheme:
examples/Node$ cat TSPostfix3.eyp
...................... # precedence declarations
%metatree
%defaultaction {
if (@_==2) { # NUM and VAR
$lhs->{t} = $_[1]->{attr};
return
}
if (@_==4) { # binary operations
$lhs->{t} = "$_[1]->{t} $_[3]->{t} $_[2]->{attr}";
return
}
die "Fatal Error. Unexpected input. Numargs = ".scalar(@_)."\n".Parse::Eyapp::Node->str(@_);
}
%%
line: %name PROG
exp <%name EXP + ';'>
{ @{$lhs->{t}} = map { $_->{t}} ($_[1]->children()); }
;
exp: %name NUM NUM
| %name VAR VAR
| %name ASSIGN VAR '=' exp { $lhs->{t} = "$_[1]->{attr} $_[3]->{t} ="; }
| %name PLUS exp '+' exp
| %name MINUS exp '-' exp
| %name TIMES exp '*' exp
| %name DIV exp '/' exp
| %name NEG '-' exp %prec NEG { $_[0]->{t} = "$_[2]->{t} NEG" }
| '(' exp ')' %begin { $_[2] }
;
%%
........................
The tree in a Translation Scheme contains the references to the CODE
implementing the semantic actions. For example, the syntax tree built by the parser for the input a=-b*3
in TSPostfix3.eyp
is:
PROG(EXP(
ASSIGN(
TERMINAL[a],
TERMINAL[=],
TIMES(
NEG(TERMINAL[-], VAR(TERMINAL[b], CODE), CODE),
TERMINAL[*],
NUM(TERMINAL[3], CODE),
CODE
) # TIMES,
CODE
) # ASSIGN
) # EXP,
CODE
) # PROG
$node->children
can also be used as a setter.
$node->Children
Returns the array of children of the node. When dealing with a translation scheme, the $node->Children
method (Notice the case difference with $node->children
, first in uppercase) returns the non CODE
children of the node. The following execution with the debugger of the example in examples/Node/ts_with_ast.pl
illustrates the difference:
examples/Node$ perl -wd ts_with_ast.pl
main::(ts_with_ast.pl:6): my $translationscheme = q{
main::(ts_with_ast.pl:7): %{
The $translationscheme
variable contains the code of a small calculator:
%metatree
%left '-' '+'
%left '*'
%left NEG
%%
line: %name EXP
$exp { $lhs->{n} = $exp->{n} }
;
exp:
%name PLUS
exp.left '+' exp.right
{ $lhs->{n} .= $left->{n} + $right->{n} }
| %name TIMES
exp.left '*' exp.right
{ $lhs->{n} = $left->{n} * $right->{n} }
| %name NUM $NUM
{ $lhs->{n} = $NUM->{attr} }
| '(' $exp ')' %begin { $exp }
| exp.left '-' exp.right
{ $lhs->{n} = $left->{n} - $right->{n} }
| '-' $exp %prec NEG
{ $lhs->{n} = -$exp->{n} }
;
We run the program with input 2+(3)
and stop it at line 88, just after the augmented AST (CODE
node included) has been built:
DB<1> c 88
main::(ts_with_ast.pl:88): $t->translation_scheme;
Now, let us see the difference between the methods children
and Children
:
DB<2> @a = $t->children; @b = $t->Children
DB<3> print Parse::Eyapp::Node::str($_)."\n" for @a
PLUS(NUM(TERMINAL,CODE),TERMINAL,NUM(TERMINAL,CODE),CODE)
CODE
DB<4> print $_->str."\n" for @b
PLUS(NUM(TERMINAL,CODE),TERMINAL,NUM(TERMINAL,CODE),CODE)
DB<5>
$node->last_child
Return the last child of the node. When dealing with translation schemes, the last can be a CODE
node.
$node->Last_child
The $node->Last_child
method returns the last non CODE child of the node. See an example:
examples/Node$ cat -n trans_scheme_default_action.pl
1 #!/usr/bin/perl -w
2 use strict;
3 use Data::Dumper;
4 use Parse::Eyapp;
5 use IO::Interactive qw(is_interactive);
6
7 my $translationscheme = q{
8 %{
9 # head code is available at tree construction time
10 use Data::Dumper;
11 our %sym; # symbol table
12 %}
13
14 %prefix Calc::
15
16 %defaultaction {
17 $lhs->{n} = eval " $left->{n} $_[2]->{attr} $right->{n} "
18 }
19
20 %metatree
21
22 %right '='
23 %left '-' '+'
24 %left '*' '/'
25
26 %%
27 line: %name EXP
28 exp <+ ';'> /* Expressions separated by semicolons */
29 { $lhs->{n} = $_[1]->Last_child->{n} }
30 ;
31
32 exp:
33 %name PLUS
34 exp.left '+' exp.right
35 | %name MINUS
36 exp.left '-' exp.right
37 | %name TIMES
38 exp.left '*' exp.right
39 | %name DIV
40 exp.left '/' exp.right
41 | %name NUM
42 $NUM
43 { $lhs->{n} = $NUM->{attr} }
44 | '(' $exp ')' %begin { $exp }
45 | %name VAR
46 $VAR
47 { $lhs->{n} = $sym{$VAR->{attr}}->{n} }
48 | %name ASSIGN
49 $VAR '=' $exp
50 { $lhs->{n} = $sym{$VAR->{attr}}->{n} = $exp->{n} }
51
52 ;
53
54 %%
55 # tail code is available at tree construction time
......................................................
77 }; # end translation scheme
78
......................................................
The node associated with $_[1]
in
27 line: %name EXP
28 exp <+ ';'> /* Expressions separated by semicolons */
29 { $lhs->{n} = $_[1]->Last_child->{n} }
is associated with the whole expression
exp <+ ';'>
and is a Calc::_PLUS_LIST
node. When feed with input a=3;b=4
the children are the two Calc::ASSIGN
subtrees associated with a=3
and b=4
and the CODE
associated with the semantic action:
{ $lhs->{n} = $_[1]->Last_child->{n} }
Using Last_child
we are avoiding the last CODE
child and setting the n
(umeric) attribute of the EXP
node to the one associated with b=4
(i.e. 4
).
examples/Node$ trans_scheme_default_action.pl
Write a sequence of arithmetic expressions: a=3;b=4
***********Tree*************
Calc::EXP(
Calc::_PLUS_LIST(
Calc::ASSIGN(
Calc::TERMINAL,
Calc::TERMINAL,
Calc::NUM(
Calc::TERMINAL,
CODE
),
CODE
) # Calc::ASSIGN,
Calc::ASSIGN(
Calc::TERMINAL,
Calc::TERMINAL,
Calc::NUM(
Calc::TERMINAL,
CODE
),
CODE
) # Calc::ASSIGN
) # Calc::_PLUS_LIST,
CODE
) # Calc::EXP
******Symbol table**********
{
'a' => { 'n' => '3' },
'b' => { 'n' => '4' }
}
************Result**********
4
$node->descendant
The descendant
method returns the descendant of a node given its coordinates. The coordinates of a node $s
relative to a tree $t
to which it belongs is a string of numbers separated by dots like ".1.3.2"
which denotes the child path from $t
to $s
, i.e. $s == $t->child(1)->child(3)->child(2)
.
See a session with the debugger:
DB<7> x $t->child(0)->child(0)->child(1)->child(0)->child(2)->child(1)->str
0 '
BLOCK[8:4:test]^{0}(
CONTINUE[10,10]
)
DB<8> x $t->descendant('.0.0.1.0.2.1')->str
0 '
BLOCK[8:4:test]^{0}(
CONTINUE[10,10]
$node->str
The str
method returns a string representation of the tree. The str method traverses the syntax tree dumping the type of the node being visited in a string. To be specific the value returned by the function referenced by $CLASS_HANDLER
will be dumped. The default value fo such function is to return the type of the node. If the node being visited has a method info
it will be executed and its result inserted between $DELIMITER
s into the string. Thus, in the "SYNOPSIS" example, by adding the info
method to the class TERMINAL
:
sub TERMINAL::info {
$_[0]{attr}
}
we achieve the insertion of attributes in the string being built by str
.
The existence of some methods (like footnote
) and the values of some package variables influence the behavior of str
. Among the most important are:
@PREFIXES = qw(Parse::Eyapp::Node::); # Prefixes to supress
$INDENT = 0; # -1 compact, no info, no footnotes
# 0 = compact, 1 = indent, 2 = indent and include Types in closing parenthesis
$STRSEP = ','; # Separator between nodes, by default a comma
$DELIMITER = '['; # The string returned by C<info> will be enclosed
$FOOTNOTE_HEADER = "\n---------------------------\n";
$FOOTNOTE_SEP = ")\n";
$FOOTNOTE_LEFT = '^{'; # Left delimiter for a footnote number
$FOOTNOTE_RIGHT = '}'; # Right delimiter for a footnote number
$LINESEP = 4; # When indent=2 the enclosing parenthesis will be
# commented if more than $LINESEP apart
$CLASS_HANDLER = sub { type($_[0]) }; # What to print to identify the node
Footnotes and attribute info will not be inserted when $INDENT
is -1. A compact representation will be obtained. Such representation can be feed to new
or hnew
to obtain a copy of the tree. See the following session with the debugger:
pl@nereida:~/LEyapp$ perl -MParse::Eyapp::Node -wde 0
main::(-e:1): 0
DB<1> $x = Parse::Eyapp::Node->new('A(B(C,D),D)', sub { $_->{order} = $i++ for @_; })
DB<2> *A::info = *B::info = *C::info = *D::info = sub { shift()->{order} }
DB<3> p $x->str
A[0](B[1](C[2],D[3]),D[4])
DB<4> $Parse::Eyapp::Node::INDENT=-1
DB<5> p $x->str
A(B(C,D),D)
DB<6> x Parse::Eyapp::Node->hnew($x->str)
0 A=HASH(0x8574704)
'children' => ARRAY(0x85745d8)
0 B=HASH(0x857468c)
'children' => ARRAY(0x8574608)
0 C=HASH(0x85745b4)
'children' => ARRAY(0x8509670)
empty array
1 D=HASH(0x8574638)
'children' => ARRAY(0x857450c)
empty array
1 D=HASH(0x8574638)
-> REUSED_ADDRESS
1 B=HASH(0x857468c)
-> REUSED_ADDRESS
2 C=HASH(0x85745b4)
-> REUSED_ADDRESS
3 D=HASH(0x8574638)
-> REUSED_ADDRESS
4 D=HASH(0x8574638)
-> REUSED_ADDRESS
The following list defines the $DELIMITER
s you can choose for attribute representation:
'[' => ']', '{' => '}', '(' => ')', '<' => '>'
If the node being visited has a method footnote
, the string returned by the method will be concatenated at the end of the string as a footnote. The variables $FOOTNOTE_LEFT
and $FOOTNOTE_RIGHT
govern the displaying of footnote numbers.
Follows an example of output using footnotes
.
nereida:~/doc/casiano/PLBOOK/PLBOOK/code/Simple-Types/script> \
usetypes.pl prueba24.c
PROGRAM^{0}(FUNCTION[f]^{1}(RETURNINT(TIMES(INUM(TERMINAL[2:2]),VAR(TERMINAL[a:2])))))
---------------------------
0)
Types:
$VAR1 = {
'CHAR' => bless( {
'children' => []
}, 'CHAR' ),
'VOID' => bless( {
'children' => []
}, 'VOID' ),
'INT' => bless( {
'children' => []
}, 'INT' ),
'F(X_1(INT),INT)' => bless( {
'children' => [
bless( {
'children' => [
$VAR1->{'INT'}
]
}, 'X_1' ),
$VAR1->{'INT'}
]
}, 'F' )
};
Symbol Table:
$VAR1 = {
'f' => {
'type' => 'F(X_1(INT),INT)',
'line' => 1
}
};
---------------------------
1)
$VAR1 = {
'a' => {
'type' => 'INT',
'param' => 1,
'line' => 1
}
};
The first footnote was due to a call to PROGRAM:footnote
. The footnote
method for the PROGRAM
node was defined as:
nereida:~/doc/casiano/PLBOOK/PLBOOK/code/Simple-Types/lib/Simple> \
sed -n -e '691,696p' Types.eyp | cat -n
1 sub PROGRAM::footnote {
2 return "Types:\n"
3 .Dumper($_[0]->{types}).
4 "Symbol Table:\n"
5 .Dumper($_[0]->{symboltable})
6 }
The second footnote was produced by the existence of a FUNCTION::footnote
method:
nereida:~/doc/casiano/PLBOOK/PLBOOK/code/Simple-Types/lib/Simple> \
sed -n -e '702,704p' Types.eyp | cat -n
1 sub FUNCTION::footnote {
2 return Dumper($_[0]->{symboltable})
3 }
The source program for the example was:
1 int f(int a) {
2 return 2*a;
3 }
$node->equal
A call $tree1->equal($tree2)
compare the two trees $tree1
and $tree2
. Two trees are considered equal if their root nodes belong to the same class, they have the same number of children and the children are (recursively) equal.
In Addition to the two trees the programmer can specify pairs attribute_key => equality_handler
:
$tree1->equal($tree2, attr1 => \&handler1, attr2 => \&handler2, ...)
In such case the definition of equality is more restrictive: Two trees are considered equal if
Their root nodes belong to the same class,
They have the same number of children
For each of the specified attributes occur that for both nodes the existence and definition of the key is the same
Assuming the key exists and is defined for both nodes, the equality handlers return true for each of its attributes and
The respective children are (recursively) equal.
An attribute handler receives as arguments the values of the attributes of the two nodes being compared and must return true if, and only if, these two attributes are considered equal. Follows an example:
examples/Node$ cat -n equal.pl
1 #!/usr/bin/perl -w
2 use strict;
3 use Parse::Eyapp::Node;
4
5 my $string1 = shift || 'ASSIGN(VAR(TERMINAL))';
6 my $string2 = shift || 'ASSIGN(VAR(TERMINAL))';
7 my $t1 = Parse::Eyapp::Node->new($string1, sub { my $i = 0; $_->{n} = $i++ for @_ });
8 my $t2 = Parse::Eyapp::Node->new($string2);
9
10 # Without attributes
11 if ($t1->equal($t2)) {
12 print "\nNot considering attributes: Equal\n";
13 }
14 else {
15 print "\nNot considering attributes: Not Equal\n";
16 }
17
18 # Equality with attributes
19 if ($t1->equal($t2, n => sub { return $_[0] == $_[1] })) {
20 print "\nConsidering attributes: Equal\n";
21 }
22 else {
23 print "\nConsidering attributes: Not Equal\n";
24 }
When the former program is run without arguments produces the following output:
examples/Node$ equal.pl
Not considering attributes: Equal
Considering attributes: Not Equal
Using equal
During Testing
During the development of your compiler you add new stages to the existing ones. The consequence is that the AST is decorated with new attributes. Unfortunately, this implies that tests you wrote using is_deeply
and comparisons against formerly correct abstract syntax trees are no longer valid. This is due to the fact that is_deeply
requires both tree structures to be equivalent in every detail and that our new code produces a tree with new attributes.
Instead of is_deeply
use the equal
method to check for partial equivalence between abstract syntax trees. You can follow these steps:
Dump the tree for the source inserting
Data::Dumper
statementsCarefully check that the tree is really correct
Decide which attributes will be used for comparison
Write the code for the expected value editing the output produced by
Data::Dumper
Write the handlers for the attributes you decided. Write the comparison using
equal
.
Tests using this methodology will not fail even if later code decorating the AST with new attributes is introduced.
See an example that checks an abstract syntax tree produced by the simple compiler (see examples/typechecking/Simple-Types-XXX.tar.gz
) for a really simple source:
Simple-Types/script$ cat prueba27.c
int f() {
}
The first thing is to obtain a description of the tree, that can be done executing the compiler under the control of the perl debugger, stopping just after the tree has been built and dumping the tree with Data::Dumper:
pl@nereida:~/Lbook/code/Simple-Types/script$ perl -wd usetypes.pl prueba27.c
main::(usetypes.pl:5): my $filename = shift || die "Usage:\n$0 file.c\n";
DB<1> c 12
main::(usetypes.pl:12): Simple::Types::show_trees($t, $debug);
DB<2> use Data::Dumper
DB<3> $Data::Dumper::Purity = 1
DB<4> p Dumper($t)
$VAR1 = bless( {
..............................................
}, 'PROGRAM' );
...............................................................
Once we have the shape of a correct tree we can write our tests:
examples/Node$ cat -n testequal.pl
1 #!/usr/bin/perl -w
2 use strict;
3 use Parse::Eyapp::Node;
4 use Data::Dumper;
5 use Data::Compare;
6
7 my $debugging = 0;
8
9 my $handler = sub {
10 print Dumper($_[0], $_[1]) if $debugging;
11 Compare($_[0], $_[1])
12 };
13
14 my $t1 = bless( {
15 'types' => {
16 'CHAR' => bless( { 'children' => [] }, 'CHAR' ),
17 'VOID' => bless( { 'children' => [] }, 'VOID' ),
18 'INT' => bless( { 'children' => [] }, 'INT' ),
19 'F(X_0(),INT)' => bless( {
20 'children' => [
21 bless( { 'children' => [] }, 'X_0' ),
22 bless( { 'children' => [] }, 'INT' ) ]
23 }, 'F' )
24 },
25 'symboltable' => { 'f' => { 'type' => 'F(X_0(),INT)', 'line' => 1 } },
26 'lines' => 2,
27 'children' => [
28 bless( {
29 'symboltable' => {},
30 'fatherblock' => {},
31 'children' => [],
32 'depth' => 1,
33 'parameters' => [],
34 'function_name' => [ 'f', 1 ],
35 'symboltableLabel' => {},
36 'line' => 1
37 }, 'FUNCTION' )
38 ],
39 'depth' => 0,
40 'line' => 1
41 }, 'PROGRAM' );
42 $t1->{'children'}[0]{'fatherblock'} = $t1;
43
44 # Tree similar to $t1 but without some attributes (line, depth, etc.)
45 my $t2 = bless( {
46 'types' => {
47 'CHAR' => bless( { 'children' => [] }, 'CHAR' ),
48 'VOID' => bless( { 'children' => [] }, 'VOID' ),
49 'INT' => bless( { 'children' => [] }, 'INT' ),
50 'F(X_0(),INT)' => bless( {
51 'children' => [
52 bless( { 'children' => [] }, 'X_0' ),
53 bless( { 'children' => [] }, 'INT' ) ]
54 }, 'F' )
55 },
56 'symboltable' => { 'f' => { 'type' => 'F(X_0(),INT)', 'line' => 1 } },
57 'children' => [
58 bless( {
59 'symboltable' => {},
60 'fatherblock' => {},
61 'children' => [],
62 'parameters' => [],
63 'function_name' => [ 'f', 1 ],
64 }, 'FUNCTION' )
65 ],
66 }, 'PROGRAM' );
67 $t2->{'children'}[0]{'fatherblock'} = $t2;
68
69 # Tree similar to $t1 but without some attributes (line, depth, etc.)
70 # and without the symboltable and types attributes used in the comparison
71 my $t3 = bless( {
72 'types' => {
73 'CHAR' => bless( { 'children' => [] }, 'CHAR' ),
74 'VOID' => bless( { 'children' => [] }, 'VOID' ),
75 'INT' => bless( { 'children' => [] }, 'INT' ),
76 'F(X_0(),INT)' => bless( {
77 'children' => [
78 bless( { 'children' => [] }, 'X_0' ),
79 bless( { 'children' => [] }, 'INT' ) ]
80 }, 'F' )
81 },
82 'children' => [
83 bless( {
84 'symboltable' => {},
85 'fatherblock' => {},
86 'children' => [],
87 'parameters' => [],
88 'function_name' => [ 'f', 1 ],
89 }, 'FUNCTION' )
90 ],
91 }, 'PROGRAM' );
92
93 $t3->{'children'}[0]{'fatherblock'} = $t2;
94
95 # Without attributes
96 if (Parse::Eyapp::Node::equal($t1, $t2)) {
97 print "\nNot considering attributes: Equal\n";
98 }
99 else {
100 print "\nNot considering attributes: Not Equal\n";
101 }
102
103 # Equality with attributes
104 if (Parse::Eyapp::Node::equal(
105 $t1, $t2,
106 symboltable => $handler,
107 types => $handler,
108 )
109 ) {
110 print "\nConsidering attributes: Equal\n";
111 }
112 else {
113 print "\nConsidering attributes: Not Equal\n";
114 }
115
116 # Equality with attributes
117 if (Parse::Eyapp::Node::equal(
118 $t1, $t3,
119 symboltable => $handler,
120 types => $handler,
121 )
122 ) {
123 print "\nConsidering attributes: Equal\n";
124 }
125 else {
126 print "\nConsidering attributes: Not Equal\n";
127 }
The code defining tree $t1
was obtained from an output using Data::Dumper
. The code for trees $t2
and $t3
was written using cut-and-paste from $t1
. They have the same shape than $t1
but differ in their attributes. Tree $t2
shares with $t1
the attributes symboltable
and types
used in the comparison and so equal
returns true
when compared. Since $t3
differs from $t1
in the attributes symboltable
and types
the call to equal
returns false
.
$node->delete
The $node->delete($child)
method is used to delete the specified child of $node
. The child to delete can be specified using the index or a reference. It returns the deleted child.
Throws an exception if the object can't do children
or has no children
. See also the delete method of treeregexes (Parse::Eyapp:YATW
objects) to delete the node being visited.
The following example moves out of a loop an assignment statement assuming is an invariant of the loop. To do it, it uses the delete
and insert_before
methods:
nereida:~/src/perl/YappWithDefaultAction/examples> \
sed -ne '98,113p' moveinvariantoutofloopcomplexformula.pl
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);
}
},
FIRSTLINE => 99,
);
$p->generate();
$moveinvariant->s($t);
The example below deletes CODE nodes from the tree build for a translation scheme:
my $transform = Parse::Eyapp::Treeregexp->new(
STRING=>q{
delete_code: CODE => { Parse::Eyapp::Node::delete($CODE) }
},
)
Observe how delete is called as a subroutine.
$node->unshift($newchild)
Inserts $newchild
at the beginning of the list of children of $node
. See also the unshift method for Parse::Eyapp:YATW
treeregexp transformation objects
$node->push($newchild)
Inserts $newchild
at the end of the list of children of $node
.
$node->insert_before($position, $new_child)
Inserts $newchild
before $position
in the list of children of $node
. Variable $position
can be an index or a reference.
The method throws an exception if $position
is an index and is not in range. Also if $node
has no children.
The method throws a warning if $position
is a reference and does not define an actual child. In such case $new_child
is not inserted.
See also the insert_before method for Parse::Eyapp:YATW
treeregexp transformation objects
$node->insert_after($position, $new_child)
Inserts $newchild
after $position
in the list of children of $node
. Variable $position
can be an index or a reference.
The method throws an exception if $position
is an index and is not in the range of $node-
children>.
The method throws a warning if $position
is a reference and does not exists in the list of children. In such case $new_child
is not inserted.
$node->translation_scheme
Traverses $node
. Each time a CODE node is visited the subroutine referenced is called with arguments the node and its children. Usually the code will decorate the nodes with new attributes or will update existing ones. Obviously this method does nothing for an ordinary AST. It is used after compiling an Eyapp program that makes use of the %metatree
directive. (See examples/Node/TSPostfix3.eyp
for an example).
$node->bud(@transformations)
Bottom-up decorator. The tree is traversed bottom-up. The set of transformations in @transformations
is applied to each node in the tree referenced by $node
in the order supplied by the user. As soon as one succeeds no more transformations are applied.
For an example see the files lib/Simple/Types.eyp
and lib/Simple/Trans.trg
in examples/typechecking/Simple-Types-XXX.tar.gz
shows an extract of the type-checking phase of a toy-example compiler:
examples/typechecking/Simple-Types-0.4/lib/Simple$ sed -ne '600,613p' Types.eyp
my @typecheck = ( # Check typing transformations for
our $inum, # - Numerical constantss
our $charconstant, # - Character constants
our $bin, # - Binary Operations
our $arrays, # - Arrays
our $assign, # - Assignments
our $control, # - Flow control sentences
our $functioncall, # - Function calls
our $statements, # - Those nodes with void type
# (STATEMENTS, PROGRAM, etc.)
our $returntype, # - Return
);
$t->bud(@typecheck);
You can find another example of use of bud
in the file examples/ParsingStringsAndTrees/infix2pir.pl
Parse::Eyapp:YATW Methods
Parse::Eyapp:YATW
objects represent tree transformations. They carry the information of what nodes match and how to modify them.
Parse::Eyapp::YATW->new
Builds a treeregexp transformation object. Though usually you build a transformation by means of Treeregexp programs you can directly invoke the method to build a tree transformation. A transformation object can be built from a function that conforms to the YATW tree transformation call protocol (see the section "The YATW Tree Transformation Call Protocol"). Follows an example (file examples/12ts_simplify_with_s.pl
):
nereida:~/src/perl/YappWithDefaultAction/examples> \
sed -ne '68,$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\n"; print "2*-3\n"; # Set the input
20 my $t = $parser->Run; # Parse it
21 print $t->str."\n";
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."\n";
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 "\n***** Before ******\n";
29 print $t->str;
30 my $p = Parse::Eyapp::YATW->new(PATTERN => \&is_foldable);
31 $p->s($t);
32 print "\n***** After ******\n";
33 print $t->str."\n";
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\n"; print $parser->YYData->{INPUT};
19 my $t = $parser->Run; # Parse it
20 print $t->str."\n"; # Show the tree
21 my $p = Parse::Eyapp::YATW->new(PATTERN => \¬_useful);
22 $p->s($t); # Delete nodes
23 print $t->str."\n"; # Show the tree
when executed we get the following output:
pl@nereida:~/src/perl/YappWithDefaultAction/examples$ 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
Tha 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\n"; print $parser->YYData->{INPUT}; # Set the input
34 my $t = $parser->Run; # Parse it
35 print $t->str."\n"; # Show the tree
36 # Get the AST
37 our ($delete_tokens, $delete_code);
38 $t->s($delete_tokens, $delete_code);
39 print $t->str."\n"; # Show the tree
40 our $insert_child;
41 $insert_child->s($t);
42 print $t->str."\n"; # Show the tree
When is executed the program produces the following output:
pl@nereida:~/src/perl/YappWithDefaultAction/examples$ 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 }\n"
is transformed in s.t. like:
"a =1000; c = 1; b = 5; while (a) { c = c*a; a = a-1 }\n"
TREE MATCHING AND TREE SUBSTITUTION
See the documentation in Parse::Eyapp::MatchingTrees
SEE ALSO
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
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/languageintro.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/debuggingtut.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/eyapplanguageref.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/Treeregexp.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/Node.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/YATW.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/Eyapp.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/Base.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/translationschemestut.pdf
The pdf file in http://nereida.deioc.ull.es/~pl/perlexamples/MatchingTrees.pdf
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/perldoc eyapp,
perldoc treereg,
perldoc vgg,
The Syntax Highlight file for vim at http://www.vim.org/scripts/script.php?script_id=2453 and http://nereida.deioc.ull.es/~vim/
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.
Man pages of yacc(1) and bison(1), http://www.delorie.com/gnu/docs/bison/bison.html
ocamlyacc tutorial at http://plus.kaist.ac.kr/~shoh/ocaml/ocamllex-ocamlyacc/ocamlyacc-tutorial/ocamlyacc-tutorial.html
REFERENCES
The classic Dragon's book Compilers: Principles, Techniques, and Tools by Alfred V. Aho, Ravi Sethi and Jeffrey D. Ullman (Addison-Wesley 1986)
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
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. Special thanks to my family and Larry Wall.
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.