#!/usr/bin/perl -w
use strict;
#use Test::More qw(no_plan);
use Test::More tests => 2;
use_ok qw(Parse::Eyapp) or exit;
my $grammar = q{
%{
#use Data::Dumper;
%}
%right '='
%left '-' '+'
%left '*' '/'
%left NEG
%tree
%%
line: exp { $_[1] }
;
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 {
exists $_[0]->YYData->{ERRMSG}
and do {
print $_[0]->YYData->{ERRMSG};
delete $_[0]->YYData->{ERRMSG};
return;
};
print "Syntax error.\n";
}
sub _Lexer {
my($parser)=shift;
$parser->YYData->{INPUT}
or $parser->YYData->{INPUT} = <STDIN>
or return('',undef);
$parser->YYData->{INPUT}=~s/^\s+//;
for ($parser->YYData->{INPUT}) {
s/^([0-9]+(?:\.[0-9]+)?)//
and return('NUM',$1);
s/^([A-Za-z][A-Za-z0-9_]*)//
and return('VAR',$1);
s/^(.)//s
and return($1,$1);
}
}
sub Run {
my($self)=shift;
$self->YYParse( yylex => \&_Lexer, yyerror => \&_Error,
#yydebug =>0xFF
);
}
}; # end grammar
my %BinaryOperation = (PLUS=>'+', MINUS => '-', TIMES=>'*', DIV => '/');
sub constant_folding {
my $left = $_[0]->child(0);
my $right = $_[0]->child(1);
defined $BinaryOperation{ref($_[0])}
and $left->isa('NUM')
and $right->isa('NUM') and do {
my $leftnum = $left->child(0)->{attr};
my $rightnum = $right->child(0)->{attr};
my $op = $BinaryOperation{ref($_[0])};
$_[0] = $left;
$left->child(0)->{attr} = eval "$leftnum $op $rightnum";
return 1;
};
return 0;
}
sub multiply_by_zero {
return 0 unless $_[0]->isa('TIMES');
return 1 if $_[0]->child(0)->isa('NUM')
and $_[0]->child(0)->child(0)->{attr} == 0
and $_[0] = $_[0]->child(0); # action: new node is zero
return 1 if $_[0]->child(1)->isa('NUM')
and $_[0]->child(1)->child(0)->{attr} == 0
and $_[0] = $_[0]->child(1); # modify node: new node is zero
return 0; # Is times but does not match: a *4 or a * b, etc.
}
#$Data::Dumper::Indent = 1;
Parse::Eyapp->new_grammar(input=>$grammar, classname=>'Rule6');
my $parser = new Rule6();
$parser->YYData->{INPUT} = "2*3+b*0\n";
my $t = $parser->Run;
$t->s(\&constant_folding, \&multiply_by_zero);
my $expected_result = bless( {
'children' => [ bless( { 'children' => [], 'attr' => 6, 'token' => 'NUM' }, 'TERMINAL' ) ]
}, 'NUM' );
is_deeply($t, $expected_result, 'hand made folding and multiply by zero');