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How Perl6 treating decimals as rationals helped me solve a problem

by grondilu (Friar)
on Nov 16, 2012 at 00:04 UTC ( #1004081=perlmeditation: print w/replies, xml ) Need Help??

Hi monks,

I was about to solve this rosalind.info problem using perl5, but while I was writing I realized there were at least two features in Perl6 that could be usefull if I want to spare a few lines of code.

So I wrote my solution in Perl6, and it passed on first try. Execution took a bit of time (about a minute or so) but it was well in the five minutes delay so that was fine. It was pretty easy. About ten lines of code.

On rosalind, once you solved a problem you can join a discussion thread where you can post your solution and see other people's ones, with comments. So I did that as I do usually.

And then I was intrigued because most people were complaining about how this problem was a pain in the xxx because of the floating point approximations.

At first I did not understand. But then, thinking about it, I realised that this problem indeed requires computing a lot of differences between decimal numbers and then comparing those differences. It sure is the kind of things that creates issues when using floating point numbers.

Yet I had totally failed to notice that this problem could occur. So how was it possible that my code worked?

Well, I then remember that Perl6 treats decimals as rationals, not floating points, and I guessed this was the answer.

I also remember that I once wondered if that was not a bit of a luxury to do that in Perl6. But now I'm totally convinced it is a good idea. A decimal should really be treated as a rational, unless explicitly casted otherwise.

I won't say that's the first time Perl6 impresses me. But hey, kind of.

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Re: How Perl6 treating decimals as rationals helped me solve a problem
by choroba (Bishop) on Nov 16, 2012 at 01:57 UTC
    Grr, do I really have to solve all the simple problems first? :-)
    لսႽ ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

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[Corion]: 1nickt: I imagine (heh) that Agile done somewhat right will make the process (and why we postpone things) somewhat more explicit to the outsider, or at least the "who do we ask to postpone X"

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