<div dir="ltr"><div dir="ltr">I submitted <a href="https://gitlab.haskell.org/ghc/ghc/merge_requests/644">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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-kt">Foldable</span> <span class="gmail-p">((,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span><span class="gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-kt">Foldable</span> <span class="gmail-p">((,,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span> <span class="gmail-n">c</span><span class="gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-kt">Traversable</span> <span class="gmail-p">((,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span><span class="gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-kt">Traversable</span> <span class="gmail-p">((,,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span> <span class="gmail-n">c</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-kt">Functor</span> <span class="gmail-p">((,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p">(</span><span class="gmail-kt">Monoid</span> <span class="gmail-n">a</span><span class="gmail-p">,</span> <span class="gmail-kt">Monoid</span> <span class="gmail-n">b</span><span class="gmail-p">)</span> <span class="gmail-o">=></span> <span class="gmail-kt">Applicative</span> <span class="gmail-p">((,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p">(</span><span class="gmail-kt">Monoid</span> <span class="gmail-n">a</span><span class="gmail-p">,</span> <span class="gmail-kt">Monoid</span> <span class="gmail-n">b</span><span class="gmail-p">)</span> <span class="gmail-o">=></span> <span class="gmail-kt">Monad</span> <span class="gmail-p">((,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-kt">Functor</span> <span class="gmail-p">((,,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span> <span class="gmail-n">c</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p">(</span><span class="gmail-kt">Monoid</span> <span class="gmail-n">a</span><span class="gmail-p">,</span> <span class="gmail-kt">Monoid</span> <span class="gmail-n">b</span><span class="gmail-p">,</span> <span class="gmail-kt">Monoid</span> <span class="gmail-n">c</span><span class="gmail-p">)</span> <span class="gmail-o">=></span> <span class="gmail-kt">Applicative</span> <span class="gmail-p">((,,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span> <span class="gmail-n">c</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p">(</span><span class="gmail-kt">Monoid</span> <span class="gmail-n">a</span><span class="gmail-p">,</span> <span class="gmail-kt">Monoid</span> <span class="gmail-n">b</span><span class="gmail-p">,</span> <span class="gmail-kt">Monoid</span> <span class="gmail-n">c</span><span class="gmail-p">)</span> <span class="gmail-o">=></span> <span class="gmail-kt">Monad</span> <span class="gmail-p">((,,,)</span> <span class="gmail-n">a</span> <span class="gmail-n">b</span> <span class="gmail-n">c</span><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-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-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-p"><code><span class="gmail-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>