CCing Michael in case this is something Conduit related that he recognizes. Ben Gamari writes:

北原真一 writes:

...

I am asking for help I am Haskeller of Japan I'm using GHC7.6.3 GHC has caused the panic https://gist.github.com/minamiyama1994/6697c3fb9c345da6715f

I can reproduce the issue on my end with 7.6.3. Setting -fsimpl-tick-factor=10000 allows the build to proceed. This is a bit odd as I don't see anything in your code that should give the simplifier too much grief, but I could be missing something. Unless you intend on releasing the code I would probably add a 'Ghc-Options: -fsimpl-tick-factor=1000' to your Cabal file for now.

That being said, the Core here does look a bit concerning with blocks of this nature being replicated 255 times (with both tick factors of 1000 and 2000), a2_rzJz a2_rzJz = \ @ a_X7Iy eta_X7IA _ _ eta3_B1 -> (# eta3_B1, eta_X7IA #) lvl24_rzJA lvl24_rzJA = IOError (Nothing) NoSuchThing getEnv3 getEnv2 (Nothing) lvl18_rzJs lvl25_rzJB lvl25_rzJB = \ @ a_a90p @ b_a90q m_a90r k_a90s r_X93X -> let { ds_X956 ds_X956 = (m_a90r `cast` ...) r_X93X } in (\ r1_X95b s_X8Wq -> case (((ds_X956 `cast` ...) r1_X95b) `cast` ...) s_X8Wq of _ { (# ipv_X8SU, ipv1_X8SW #) -> ((((((k_a90s ipv1_X8SW) `cast` ...) r_X93X) `cast` ...) r1_X95b) `cast` ...) ipv_X8SU }) `cast` ... With associated case matches in `main` I suppose it's posssible that this is intended, although the code does seem quite bloated for such a simple program. Full Core here[1]. Cheers, - Ben [1] http://mw0.mooo.com/~ben/Main.core