Parse::Eyapp 1.069577

Parse::Eyapp module contains extensions for Parse::Yapp.

SYNOPSIS

use strict;
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 EXPRESION_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{Gs+}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);
}
}

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;--2n"; # 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";