/usr/share/doc/libparse-recdescent-perl/examples/demo_calc.pl is in libparse-recdescent-perl 1.967009+dfsg-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 | use v5.10;
use warnings;
use Parse::RecDescent;
sub evalop
{
my (@list) = @{$_[0]};
my $val = shift(@list)->();
while (@list)
{
my ($op, $arg2) = splice @list, 0, 2;
$op->($val,$arg2->());
}
return $val;
}
my $parse = Parse::RecDescent->new(<<'EndGrammar');
<trace_parse>
main: expr /\s*\Z/ { $item[1]->() }
| <error>
expr: /for(each)?/ lvar range expr
{ my ($vname,$expr) = @item[2,4];
my ($from, $to) = @{$item[3]};
sub { my $val;
no strict "refs";
for $$vname ($from->()..$to->())
{ $val = $expr->() }
return $val;
}
}
| lvar '=' addition
{ my ($vname, $expr) = @item[1,3];
sub { no strict 'refs'; $$vname = $expr->() }
}
| addition
range: "(" expr ".." expr ")"
{ [ @item[2,4] ] }
addition: <leftop:multiplication add_op multiplication>
{ my $add = $item[1]; sub { ::evalop $add } }
add_op: '+' { sub { $_[0] += $_[1] } }
| '-' { sub { $_[0] -= $_[1] } }
multiplication: <leftop:factor mult_op factor>
{ my $mult = $item[1]; sub { ::evalop $mult } }
mult_op: '*' { sub { $_[0] *= $_[1] } }
| '/' { sub { $_[0] /= $_[1] } }
factor: number
| rvar
| '(' expr ')' { $item[2] }
number: /[-+]?\d+(\.\d+)?/ { sub { $item[1] } }
lvar: /\$([a-z]\w*)/ { $1 }
rvar: lvar { sub { no strict 'refs'; ${$item[1]} } }
EndGrammar
print "> ";
while (<>) { # FOR DEMO CHANGE TO: while (<DATA>)
print $parse->main($_), "\n\n> ";
}
__DATA__
$x = 2
$y = 3
+1-1+1-1+1-1+1-1+1
7*7-6*8
121/(121/11)/121*11
1/(10-1/(1/(10-1)))
$x * $y
foreach $i (1..$y) $x = $x * 2 + $i
$x
|