Bug: GHC creates incorrect code which throws <<loop>>

Richard Eisenberg eir at cis.upenn.edu
Thu Apr 23 02:07:23 UTC 2015

Thanks for posting the bug and bringing it to our attention. The reason the report may not have gotten attention is that I believe this falls in Simon PJ's domain, and he's on holiday right now. I took a quick look, but I haven't a clue about this area of GHC, so there's not much I can contribute. Unless someone else out there knows much about black-holing, you may have to wait a bit. Sorry!


On Mar 31, 2015, at 9:48 PM, Yongqian Li <yongqli at kerrmetric.com> wrote:

> Hi all,
> I wanted to bring to your attention this bug,
> https://ghc.haskell.org/trac/ghc/ticket/10218 , which I filed about
> two days ago but hasn't gotten any replies to yet.
> In my opinion, this is a rather serious bug since GHC is producing
> incorrect code. While there is a workaround, it makes my program take
> about 2 hours to compile.
> Since reporting the bug, I've also seen "strange closure type"
> exceptions, which I believe are also caused by this bug, although I do
> not have a test case. Based on my limited understanding of GHC
> internals, I suspect the problem lies in how type class dictionaries
> are looked up at run time, as the problem disappears if GHC can fully
> resolve the types.
> Can others see if they can reproduce this bug? If there is any way I
> can help, please let me know.
> Sincerely,
> Yongqian Li
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