On Wed, Dec 5, 2012 at 8:16 AM, Henning Thielemann <span dir="ltr">&lt;<a href="mailto:lemming@henning-thielemann.de" target="_blank">lemming@henning-thielemann.de</a>&gt;</span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div id=":151">The same can be asked for<br>
<br>
Prelude&gt; :t either (const False) (const True)<br>
either (const False) (const True) :: Either a b -&gt; Bool<br>
<br>
or<br>
<br>
isLeft = isJust . maybeLeft<div class="yj6qo ajU"><div id=":1cx" class="ajR" tabindex="0"></div></div></div></blockquote></div><br><div>We at least have evidence that isLeft and isRight are actually present in several packages. That helps this proposal squeak over my bar, so I&#39;m +0 on it.</div>
<div><br></div><div>I think that maybeLeft and maybeRight are interesting, but the burden of proof for &quot;these things solve a problem that actually exists&quot; is a little higher. Consider me -0.01.</div><div><br></div>
<div>In general, I feel we have a fondness for a few too many near-trivial one-liners that make libraries bigger and harder to navigate, without really adding much expressivity.</div><div><br></div><div>For instance, aeson has a couple of combinators that are intended to help with structure access and lookup, and I&#39;ve gotten pull requests for a bunch more due to the existing precedents, but they all have me feeling that the first few were wrong and the rest are even more wrong: they don&#39;t compose. Either lenses or a little DSL would have been better choices.</div>