Hi

I always thought that codefilters are executed before any parsing, but it seems to me that the code already has to be valid before parsing or validation.

Example: The following code tries to use the character X as a new kind of sigil (for motivation please see Re^2: Two more Features Perl 5 Maybe Needs) 

#!/usr/bin/perl
no warnings;
use Filter::Simple;

my $transform = sub {
    s{ X(\w+)\[ }
     {\$$1->\[}xg;
    s{ X(\w+) }
     {\$$1}xg;
    };

FILTER_ONLY    "executable_no_comments" => $transform;


while ($line=<DATA>) {$_.=$line}


if ($_) {
    print "\nbefore:\n",$_;

    &$transform;
    print  "\nafter:\n", $_;

    print "\neval:\n";
    eval $_;
}

__DATA__
Xarr=[1..3];
print "@Xarr";

[download]
this code works as intended: 
before:
Xarr=[1..3];
print "@Xarr";

after:
$arr=[1..3];
print "@$arr";

eval:
1 2 3

[download]
but if I comment out the lines starting with while and __DATA__ to filter the code directly I get: 
Can't modify constant item in scalar assignment at /home/lanx/perl/sig
+il.pl line 29, near "];"
Execution of /home/lanx/perl/sigil.pl aborted due to compilation error
+s.

[download]
line 29 is Xarr=[1..3]; which is of course not valid before transformation.

So is it only possible to use codefilters on syntactically valid code, or did I miss a possibility to filter non-valid code before processing???

Cheers Rolf

In reply to Are codefilters restricted to valid code? by LanX

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