<div dir="ltr">Fine, let's forget about Foldable instances. What about Monad and Traversable?</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">2019年4月2日(火) 13:28 Fumiaki Kinoshita <<a href="mailto:fumiexcel@gmail.com">fumiexcel@gmail.com</a>>:<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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-kt">Foldable</span> <span class="gmail-m_-730351250232211818gmail-p">((,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-kt">Foldable</span> <span class="gmail-m_-730351250232211818gmail-p">((,,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-p">)</span></code><br></span></code></span></code></span></code></span></code></span></code></span></code></div><div><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-kt">Traversable</span> <span class="gmail-m_-730351250232211818gmail-p">((,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-kt">Traversable</span> <span class="gmail-m_-730351250232211818gmail-p">((,,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-kt">Functor</span> <span class="gmail-m_-730351250232211818gmail-p">((,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p">(</span><span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">a</span><span class="gmail-m_-730351250232211818gmail-p">,</span> <span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-p">)</span> <span class="gmail-m_-730351250232211818gmail-o">=></span> <span class="gmail-m_-730351250232211818gmail-kt">Applicative</span> <span class="gmail-m_-730351250232211818gmail-p">((,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p">(</span><span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">a</span><span class="gmail-m_-730351250232211818gmail-p">,</span> <span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-p">)</span> <span class="gmail-m_-730351250232211818gmail-o">=></span> <span class="gmail-m_-730351250232211818gmail-kt">Monad</span> <span class="gmail-m_-730351250232211818gmail-p">((,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-kt">Functor</span> <span class="gmail-m_-730351250232211818gmail-p">((,,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p">(</span><span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">a</span><span class="gmail-m_-730351250232211818gmail-p">,</span> <span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-p">,</span> <span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-p">)</span> <span class="gmail-m_-730351250232211818gmail-o">=></span> <span class="gmail-m_-730351250232211818gmail-kt">Applicative</span> <span class="gmail-m_-730351250232211818gmail-p">((,,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p">(</span><span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">a</span><span class="gmail-m_-730351250232211818gmail-p">,</span> <span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">b</span><span class="gmail-m_-730351250232211818gmail-p">,</span> <span class="gmail-m_-730351250232211818gmail-kt">Monoid</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-p">)</span> <span class="gmail-m_-730351250232211818gmail-o">=></span> <span class="gmail-m_-730351250232211818gmail-kt">Monad</span> <span class="gmail-m_-730351250232211818gmail-p">((,,,)</span> <span class="gmail-m_-730351250232211818gmail-n">a</span> <span class="gmail-m_-730351250232211818gmail-n">b</span> <span class="gmail-m_-730351250232211818gmail-n">c</span><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-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_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-p"><code><span class="gmail-m_-730351250232211818gmail-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>
</blockquote></div>