GHC: Ticket #1494: panic! (the 'impossible' happened)
http://ghc.haskell.org/trac/ghc/ticket/1494
<p>
After hours of reducing my code, I finally was able to make a small test case. I am essentially stuck if this doesn't get fixed soon.
</p>
<p>
Output:
</p>
<p>
ghc-6.7.20070702: panic! (the 'impossible' happened)
</p>
<blockquote>
<p>
(GHC version 6.7.20070702 for i386-unknown-linux):
</p>
<blockquote>
<p>
nameModule $dMonad{v a3hFy}
</p>
</blockquote>
</blockquote>
<p>
Please report this as a GHC bug: <a href="http://www.haskell.org/ghc/reportabug">http://www.haskell.org/ghc/reportabug</a>
</p>
en-usGHChttp://ghc.haskell.org/trac/ghc/chrome/site/ghc_logo.png
http://ghc.haskell.org/trac/ghc/ticket/1494
Trac 1.2.2iampure@…Wed, 04 Jul 2007 15:17:26 GMTattachment set
http://ghc.haskell.org/trac/ghc/ticket/1494
http://ghc.haskell.org/trac/ghc/ticket/1494
<ul>
<li><strong>attachment</strong>
set to <em>YetAnotherBug.hs</em>
</li>
</ul>
<p>
It should load fine in 6.7, but evaluating a, makes it panic.
</p>
TicketsimonpjWed, 04 Jul 2007 16:29:16 GMT
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:1
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:1
<p>
Thanks for the boiled-down case. I'll look into it.
</p>
<p>
So it's fine in 6.6.1, right? Can you use that meanwhile?
</p>
<p>
Simon
</p>
TicketsimonpjWed, 04 Jul 2007 17:01:05 GMT
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:2
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:2
<p>
I've boiled it down more:
</p>
<pre class="wiki">module Foo where
import Control.Monad.State
newtype L m r = L (StateT Int m r)
instance Monad m => Monad (L m)
zork :: (Monad m) => a -> L m ()
zork = undefined
mumble e = do { modify id; zork e }
</pre><p>
Compiling this with <code>-dcore-lint</code> shows the error. More anon.
</p>
<p>
Simon
</p>
Ticketiampure@…Wed, 04 Jul 2007 18:05:16 GMT
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:3
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:3
<p>
I am sure my requirements don't fit version 6.6.1. This specific code works with 6.6.1, but I reported other bugs, on which 6.6.1 doesn't suffice. I think most of those bugs have been fixed in the version I report this bug for (which is the reason I compiled 6.7), but I am positive my code base doesn't work with 6.6.1. Conclusion: this is still a blocker for me.
</p>
<p>
What is "More anon."?
</p>
TicketsimonpjThu, 05 Jul 2007 08:03:53 GMTstatus changed; testcase, resolution set
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:4
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:4
<ul>
<li><strong>testcase</strong>
set to <em>tc232</em>
</li>
<li><strong>status</strong>
changed from <em>new</em> to <em>closed</em>
</li>
<li><strong>resolution</strong>
set to <em>fixed</em>
</li>
</ul>
<p>
I've fixed this one. Thanks for a helpful report.
</p>
<p>
Simon
</p>
<ul><li>Fix Trac <a class="closed ticket" href="http://ghc.haskell.org/trac/ghc/ticket/1494" title="#1494: bug: panic! (the 'impossible' happened) (closed: fixed)">#1494</a>
</li></ul><blockquote>
<p>
A tricky bug to do with the way the implication constraints are
solved in TcSimplify. See Note [Reducing implication constraints].
</p>
</blockquote>
Ticketiampure@…Thu, 05 Jul 2007 10:35:14 GMTstatus changed; resolution deleted
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:5
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:5
<ul>
<li><strong>status</strong>
changed from <em>closed</em> to <em>reopened</em>
</li>
<li><strong>resolution</strong>
<em>fixed</em> deleted
</li>
</ul>
<p>
I was pleased to find out you had solved this so quickly, but unfortunately, I cannot build ghc from darcs now.
</p>
<p>
I did:
./darcs-all pull -a
sh boot
make
and got:
</p>
<p>
<a class="ext-link" href="http://pastebin.ca/604150"><span class="icon"></span>http://pastebin.ca/604150</a>
</p>
Ticketiampure@…Thu, 05 Jul 2007 10:37:41 GMTstatus changed; resolution set
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:6
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:6
<ul>
<li><strong>status</strong>
changed from <em>reopened</em> to <em>closed</em>
</li>
<li><strong>resolution</strong>
set to <em>fixed</em>
</li>
</ul>
<p>
Forgot trivial step in build process, my bad... building.
</p>
TicketsimonmarTue, 30 Sep 2008 15:39:42 GMTarchitecture changed
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:7
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:7
<ul>
<li><strong>architecture</strong>
changed from <em>Unknown</em> to <em>Unknown/Multiple</em>
</li>
</ul>
TicketsimonmarTue, 30 Sep 2008 15:50:49 GMTos changed
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:8
http://ghc.haskell.org/trac/ghc/ticket/1494#comment:8
<ul>
<li><strong>os</strong>
changed from <em>Unknown</em> to <em>Unknown/Multiple</em>
</li>
</ul>
Ticket