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japhygesis

by japhy (Canon)
on Jun 21, 2001 at 20:19 UTC ( #90442=perlmeditation: print w/replies, xml ) Need Help??

Perl 6, in our time. ;) I decided to take advantage of the 'bool' overloading context, and "fix" index(), rindex(), and system().
#!/usr/bin/perl -wl use TrueFalse; BEGIN { *CORE::GLOBAL::index = sub { my $pos = (@_ == 3) ? CORE::index($_[0], $_[1], $_[2]) : CORE::index($_[0], $_[1]); boolean $pos => ($pos == -1 ? false : true); }; *CORE::GLOBAL::rindex = sub { my $pos = (@_ == 3) ? CORE::rindex($_[0], $_[1], $_[2]) : CORE::rindex($_[0], $_[1]); boolean $pos => ($pos == -1 ? false : true); }; *CORE::GLOBAL::system = sub { my $ret = system(@_); boolean $ret => ($ret ? false : true); } } print "j => $x" if $x = index "jeff", "j"; print "r => $x" if $x = rindex "jeff", "r"; system "ls" or warn "ls failed";
The code behind this is rather simple -- it's just the "fixing" of the functions that looks tricky.
package TrueFalse; use overload ( '+0' => \&num, '""' => \&num, bool => \&bool, fallback => 1, ); require Exporter; @ISA = qw( Exporter ); @EXPORT = qw( boolean true false ); use constant false => 0; use constant true => 1; sub new { bless [ @_[1,2] ], $_[0] } sub bool { $_[0][1] } sub num { $_[0][0] } sub boolean { TrueFalse->new(@_) } 1;


japhy -- Perl and Regex Hacker

Replies are listed 'Best First'.
Re: japhygesis
by Abigail (Deacon) on Jun 22, 2001 at 05:51 UTC
    What follows is a module I wrote quite some time ago (as a proof of concept) that "fixes" index in a different way. It returns undef if there is no match, and the position of the match otherwise - however, if it matches at the beginning of the string, "0 but true" is returned.
    package Perl; use Exporter; use vars qw /@ISA @EXPORT @EXPORT_OK %EXPORT_TAGS/; @ISA = qw /Exporter/; @EXPORT = qw /index/; @EXPORT_OK = qw //; %EXPORT_TAGS = (); sub index { my $result; $result = 2 == @_ ? CORE::index ($_ [0], $_ [1]) : CORE::index ($_ [0], $_ [1], $_ [2]); $result < 0 ? undef : $result || "00"; } 1; __END__

    -- Abigail

      Nice, too few people realise that you can just return a string to evaluate as zero, but still be true. I often return things like "0 but true" when I want the 0 value to be true; that way you can return 0 on errors too. A little trick I picked up was if you need to print the value, you can just use "0\0" It's 0 plus the null character, so it's true, but it only prints 0.

      The 15 year old, freshman programmer,
      Stephen Rawls

        #!/usr/bin/perl -w print 0+"0 but true",$/; print 0+"0\0",$/; __END__ Argument "0" isn't numeric in addition (+) at - line 3 0 0

        Not only does it generate warnings, but they are confusing warnings. I'd probably use "00" over "0\0" if you wanted something that printed out nicer. (:

                - tye (but my friends call me "Tye")

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