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All the Perl that's Practical to Extract and Report

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Adventures in functional Perl programming: the Y combinator 6 Comments More | Login | Reply /

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  • Can you give an example of how this might make some code cleaner or more correct?

    • I had to chuckle at your subject. I certainly know the feeling. The upshot is that you can use this to write recursive anonymous closures (avoiding all side-effects).

      I did this as an excercise. I am tiptoeing into the functional world proper lately, but my stance to it remains ambivalent. Perl isn’t quite the most beautiful language, but I find it a whoooole lot easier to read than any Lisp. I doubt that will ever change, irrespective of practice – I find your lack of syntax disturbing. This

      • You would need to do:
        my $fac = do {
            my $f;
            my $tmp = $f = sub {
                my ( $n ) = @_;
                $n < 2 ? 1 : $n * $f->( $n - 1 );
            };
            weaken($f);
            $f;
        };
        If you just weaken f without the tmp variable, you lose all references to it and it goes away before you have a chance to return it.

        • Ah yes, d’uh.

          But didn’t you mean your do {} block to return $tmp rather than $f? $f is the weak reference used inside the function, while $tmp is the strong reference you pass back out to the surrounding expression, no?

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