Dear GHC developers, The confirmation token letter from the bug tracker travels too long, I do not know, why. Meanwhile I cannot report there. So, I report it in the below way: http://www.botik.ru/pub/local/Mechveliani/ghcQuest/7.10.1-errReport-may22-20... Make it, please, with ghc-7.10.1 as it is written there in install.txt, including making demotest/Main. Then ./Main breaks in the middle reporting a DoCon application error ---------------------------------------------------------------------------- Factorization in K1[x], K1 a generic finite extension of a prime field K = Z/(p) .. factor f, f = (x^10 + x^7 + x^5 + x^3 + x^2 + (2)*x+ (2)) <- K[x] = ((Z/<5>)["t"]/<(t^3 + 4*t + 3)>)["x"] Domain term of K must contain a Finite field description. --------------------------------------------------------------------------- I obtain this for ghc-7.10.1 made from source by ghc-7.8.2 on Debian Linux, x-86, 64 bit. The story is as follows. docon-2.12 http://www.botik.ru/pub/local/Mechveliani/docon/2.12/ has been tested under ghc-7.8.2, and it works. Now I am trying to port it to ghc-7.10.1. This needs inserting certain pragmas for OVERLAPPING/OVERLAPPABLE into some instance declarations. So I call this port docon-2.12.1. 7.10.1-errReport-may22-2015.zip is the error report of docon-2.12.1 to ghc-7.10.1. This application has the OVERLAPPABLE pragma set to one instance and the OVERLAPPING pragma set to many instances. GHC itself warns of overlaps. Then I 1) set the pragma to the reported instance (pair), 2) recompile the corresponding module 3) rerun make configure; make build. This process has finished in `making' the application. Then, > cd demotest > ghc $doconCpOpt -O --make -rtsopts Main > ./Main produces the above error instead of the test success report. I suspect that the reason is in treating the instance overlaps (but there may be another source). Comparing docon-2.12 + ghc-7.8.2 to 7.10.1-errReport-may22-201 + ghc-7.10.1, can you, please, find: how to fix the latter version? Is this a bug in ghc-7.10.1 ? Regards, -------- Sergei