#!/usr/bin/perl -w
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 ...
%token NUM = /([0-9]+(?:\.[0-9]+)?)/
%token VAR = /([A-Za-z][A-Za-z0-9_]*)/
%%
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 */
;
%%
}; # 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=>10, # String $grammar starts at line 10 (for error diagnostics)
#outputfile => 'main',
);
my $parser = Calc->new(); # Create a parser
$parser->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";