<div dir="ltr">I'm +1 on this on the grounds we established a few years back of adding unambigously defined instances where they are well determined.<div><br></div><div>I've gone to reach for a couple of these before being stymied by their absence in the past and had to build local data types or, worse, inflict orphans on my users.<br><div><br></div><div>-Edward</div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Apr 2, 2019 at 12:29 AM Fumiaki Kinoshita <<a href="mailto:fumiexcel@gmail.com">fumiexcel@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr">I submitted <a href="https://gitlab.haskell.org/ghc/ghc/merge_requests/644" target="_blank">https://gitlab.haskell.org/ghc/ghc/merge_requests/644</a> but it might be still controversial. I'd like to get more opinions again.<br></div><div dir="ltr"><br></div><div>Here's the list of proposed instances:</div><div><br></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-kt">Foldable</span> <span class="gmail-m_6281411910284132752gmail-p">((,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-kt">Foldable</span> <span class="gmail-m_6281411910284132752gmail-p">((,,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-kt">Traversable</span> <span class="gmail-m_6281411910284132752gmail-p">((,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-kt">Traversable</span> <span class="gmail-m_6281411910284132752gmail-p">((,,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-kt">Functor</span> <span class="gmail-m_6281411910284132752gmail-p">((,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p">(</span><span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">a</span><span class="gmail-m_6281411910284132752gmail-p">,</span> <span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span> <span class="gmail-m_6281411910284132752gmail-o">=></span> <span class="gmail-m_6281411910284132752gmail-kt">Applicative</span> <span class="gmail-m_6281411910284132752gmail-p">((,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p">(</span><span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">a</span><span class="gmail-m_6281411910284132752gmail-p">,</span> <span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span> <span class="gmail-m_6281411910284132752gmail-o">=></span> <span class="gmail-m_6281411910284132752gmail-kt">Monad</span> <span class="gmail-m_6281411910284132752gmail-p">((,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-kt">Functor</span> <span class="gmail-m_6281411910284132752gmail-p">((,,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p">(</span><span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">a</span><span class="gmail-m_6281411910284132752gmail-p">,</span> <span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">,</span> <span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span> <span class="gmail-m_6281411910284132752gmail-o">=></span> <span class="gmail-m_6281411910284132752gmail-kt">Applicative</span> <span class="gmail-m_6281411910284132752gmail-p">((,,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p">(</span><span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">a</span><span class="gmail-m_6281411910284132752gmail-p">,</span> <span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">b</span><span class="gmail-m_6281411910284132752gmail-p">,</span> <span class="gmail-m_6281411910284132752gmail-kt">Monoid</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span> <span class="gmail-m_6281411910284132752gmail-o">=></span> <span class="gmail-m_6281411910284132752gmail-kt">Monad</span> <span class="gmail-m_6281411910284132752gmail-p">((,,,)</span> <span class="gmail-m_6281411910284132752gmail-n">a</span> <span class="gmail-m_6281411910284132752gmail-n">b</span> <span class="gmail-m_6281411910284132752gmail-n">c</span><span class="gmail-m_6281411910284132752gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p"><code><span class="gmail-m_6281411910284132752gmail-p">The absence of Traversable instances for tuples feels quite inconsistent given that there are Bitraversable instances </span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code></span></code><span style="font-family:monospace">already</span>.</div></div>
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</blockquote></div>