<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><span></span></div><div><meta http-equiv="content-type" content="text/html; charset=utf-8"><div></div><div>I don't know what this means -- can you elaborate?</div><div><br></div><div>(What I'm proposing is, since there is a sizeable number of people on both sides of the issue who don't seem to be coming closer to an agreement, we bring a vote *to the users* on whether to provide Foldable/Traversable instances for tuples of size 2 and greater. If users say they're useful, we keep/add 'em. If they find them confusing/not useful, we remove/don't add 'em)</div><div><br></div><div>Tom</div><div><br></div><div><br>El 24 feb 2016, a las 12:27, Chris Allen <<a href="mailto:cma@bitemyapp.com">cma@bitemyapp.com</a>> escribió:<br><br></div><blockquote type="cite"><div>
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You can't not-include the instances because we'll just end up with
orphans so that's not cricket I think.<br>
<br>
<div class="moz-cite-prefix">On 02/24/2016 11:17 AM,
<a class="moz-txt-link-abbreviated" href="mailto:amindfv@gmail.com">amindfv@gmail.com</a> wrote:<br>
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<div>It seems like very few people are changing their minds, after
a lot of discussion -- maybe it's time to agree to disagree, in
the form of a vote on whether to include the tuple instances.</div>
<div><br>
</div>
<div> If so, I'd think we'd want to come to the users with a
discussion of both sides and a poll, a la FTP.</div>
<div><br>
</div>
<div>Tom</div>
<div><br>
</div>
<div><br>
El 24 feb 2016, a las 11:38, David Feuer <<a moz-do-not-send="true" href="mailto:david.feuer@gmail.com"></a><a class="moz-txt-link-abbreviated" href="mailto:david.feuer@gmail.com">david.feuer@gmail.com</a>>
escribió:<br>
<br>
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<blockquote type="cite">
<div>
<div dir="ltr"><br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Feb 24, 2016 at 11:22 AM,
Kosyrev Serge <span dir="ltr"><<a moz-do-not-send="true" href="mailto:_deepfire@feelingofgreen.ru" target="_blank">_deepfire@feelingofgreen.ru</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
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Are you also saying that this cannot be resolved by
some kind of a<br>
type families-based type-level 'flip'?<br>
<span class="im HOEnZb"></span></blockquote>
<div><br>
</div>
<div>It really can't, no. You can define<br>
<br>
</div>
<div>type family FlipF f a b where<br>
</div>
<div> FlipF f a b = f b a<br>
<br>
</div>
<div>but FlipF, being a type family, is not first-class.
You can't make any instances whatsoever for FlipF f a
-- you'll probably get an error about a partially
applied type family. What you *can* do is make a Flip
newtype:<br>
<br>
</div>
<div>newtype Flip f a b = Flip {unflip :: f b a}<br>
<br>
</div>
<div>This behaves perfectly:<br>
<br>
</div>
<div>instance Bifunctor f => Functor (Flip f a) where<br>
</div>
<div> fmap f = Flip . first f . unflip<br>
</div>
<div>instance Profunctor f => Contravariant (Flip f
a) where<br>
</div>
<div> contramap f = Flip . lmap f . unflip<br>
</div>
<div>instance Bifunctor f => Bifunctor (Flip f) where<br>
</div>
<div> bimap f g (Flip x) = Flip (bimap g f x)<br>
</div>
</div>
</div>
</div>
</div>
</blockquote>
<blockquote type="cite">
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