<div dir="ltr">Hi,<div><br></div><div>oh, I didn't realize that you meant using HEAD.</div><div><br></div><div>I'd guess that the new behavior is a result of the changes Simon made to the constraint solver a little while ago (maybe about a month ago?). </div>
<div>I haven't had a chance to look at the code yet, but I believe he eliminated some constraint interactions, which did not contribute towards type-checking more programs, but lead to more confusing error messages.</div>
<div><font face="arial, helvetica, sans-serif"><br></font></div><div><font face="arial, helvetica, sans-serif">By the way, I am not sure that this is a regression---I kind of like new the new behavior. For my second example we get:</font></div>
<div><font face="arial, helvetica, sans-serif"><br></font></div><div><font face="courier new, monospace">test.hs:9:8:</font></div><div><font face="courier new, monospace"> No instance for (C Bool Float) arising from a use of ‛op’</font></div>
<div><font face="courier new, monospace"> In the expression: op True :: Float</font></div><div><font face="courier new, monospace"> In an equation for ‛test’: test = op True :: Float</font></div><div><br></div><div>
This tells us exactly what the problem is, namely the missing instance, without going into stuff about functional dependencies. I guess we _could_ also say that such an instance can't exist because of the other instance and the functional dependency, but I am not sure how relevant that is...</div>
<div><br></div><div>-Iavor</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Dec 3, 2013 at 1:40 PM, Joachim Breitner <span dir="ltr"><<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Hi,<br>
<br>
Am Dienstag, den 03.12.2013, 11:08 -0800 schrieb Iavor Diatchki:<br>
<div class="im"><br>
> Here is a piece of code that produces the desired error:<br>
><br>
</div>> [..]<br>
<div class="im">><br>
> The `DataKinds` and `KindSigantures` are only used to match your<br>
> example closely.<br>
> Here is a simpler version that causes essentially the same error:<br>
><br>
</div>> [..]<br>
><br>
<br>
thanks for these examples. Both, though, give different error messages<br>
in GHC HEAD. I’m more and more confident that this is an inadvertent<br>
error message, see<br>
<a href="https://ghc.haskell.org/trac/ghc/ticket/8592" target="_blank">https://ghc.haskell.org/trac/ghc/ticket/8592</a><br>
<br>
Once that is sorted out, I’ll make sure these examples (or at least a<br>
representative one) makes it into the testsuite.<br>
<div class=""><div class="h5"><br>
Greetings,<br>
Joachim<br>
<br>
<br>
--<br>
Joachim “nomeata” Breitner<br>
<a href="mailto:mail@joachim-breitner.de">mail@joachim-breitner.de</a> • <a href="http://www.joachim-breitner.de/" target="_blank">http://www.joachim-breitner.de/</a><br>
Jabber: <a href="mailto:nomeata@joachim-breitner.de">nomeata@joachim-breitner.de</a> • GPG-Key: 0x4743206C<br>
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</div></div></blockquote></div><br></div></div>