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I get this error in my program:
couchnews: internal error: MVAR_CLEAN on mutable list
(GHC version 7.0.2 for x86_64_unknown_linux)
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
zsh: abort ./couchnews
I stripped it down to a minimal example, available at http://darcsden.com/stulli/couchnews
1. compile 'couchnews.hs' with 'ghc --make -dcore-lint -debug couchnews.hs'
2. start with ./couchnews
3. move down the list 2 times with the arrow keys
4. enjoy error message shown above
I'm not sure if this a vty-ui or a vty error (or even a GHC error).
I'd like to add one thing: This bug happens also when compiling without debugging support but it's not so obvious then. In my situation i hat to keep pressing the the down arrow for about 20 seconds when the program would segfault. With help from #haskell i managed to get as far as described above.
This is some form of internal error in GHC. However it could be the result of an error in VTY. I'll check it out.
I suspect the error is in VTY's input handling layer and vty-ui.
This is already fixed in GHC 7.3.0 (HEAD). See
However, there still may be an error in vty, because in 7.3.0 similar actions trigger instead this bug:
I see something related in an old changlog entry, too:
* binding for mk_wcswidth was incorrect. Most platforms just magically worked due to
Confirmed using VTY head and vty-ui head and ghc 7.0.1. Will update with 7.2.1 now that I realized my main dev box is still using 7.0.1 O_o
vty-ui needs this minor patch:coreyoconnor/vty-ui@042d822