November 2016 - ghc-tickets

[GHC] #10420: "Care with plugin imports" is wrong / orphan RULE visibility
by GHC 29 Jan '17

29 Jan '17

#10420: "Care with plugin imports" is wrong / orphan RULE visibility -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- A module loaded by a plugin poisons the module cache, so we never load an orphan RULE or instance even if we legitimately should do so. The way to test this is a bit convoluted, but it goes something like this: plugins07.hs {{{ module Main where import Plugins07a import RuleDefiningPlugin {-# NOINLINE x #-} x = "foo" main = putStrLn (show x) }}} Plugins07a.hs {{{ --{-# OPTIONS_GHC -fplugin RuleDefiningPlugin #-} module Plugins07a where }}} RuleDefiningPlugin.hs, in ANOTHER PACKAGE (otherwise, EPT rules don't apply) {{{ module RuleDefiningPlugin where import GhcPlugins {-# RULES "unsound" forall x. show x = "SHOWED" #-} plugin :: Plugin plugin = defaultPlugin }}} I'll commit the full test. Here's what happens: * Building `Plugins07a` results in `loadPluginInterface` on `RuleDefiningPlugin`. We load the `ModIface` but only add its types to the environment because of the "Care with plugin imports" special case. * Building `plugins07.hs` results in a normal source level import for `RuleDefiningPlugin`, but `ModIface` is already in the cache so we don't load anything. RULE is not loaded, disaster! Admittedly, actually triggering this bug requires a convoluted chain of events. But really this problem arose because the "Care with plugin imports" fix is just completely nonsense. Here's what we should do: * We should apply the same fix from #2182 on orphan instances to orphan rules too. This way, we can safely load RULEs into the EPS without accidentally bringing them into scope when they shouldn't be. * Loading an interface should unconditionally suck in the instances and rules. The result is more correct and simpler, so it seems worth fixing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10420> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12661: Testsuite driver fails on Windows
by GHC 28 Jan '17

28 Jan '17

#12661: Testsuite driver fails on Windows --------------------------------------+--------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Test Suite | Version: 8.0.1 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+--------------------------------- I encountered the following failure in the testsuite driver while bringing up the new Windows build bot, {{{ PYTHON="python2" "python2" ../../driver/runtests.py -e ghc_compiler_always_flags="'-dcore-lint -dcmm-lint -no-user-package-db -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -dno- debug-output'" -e config.compiler_debugged=True -e ghc_with_native_codegen=1 -e config.have_vanilla=True -e config.have_dynamic=False -e config.have_profiling=False -e ghc_with_threaded_rts=1 -e ghc_with_dynamic_rts=0 -e config.have_interp=False -e config.unregisterised=False -e config.ghc_dynamic_by_default=False -e config.ghc_dynamic=False -e ghc_with_smp=1 -e ghc_with_llvm=0 -e windows=True -e darwin=False -e config.in_tree_compiler=True --threads=3 -e config.cleanup=True -e config.local=False --rootdir=. --configfile=../../config/ghc -e 'config.confdir="../../config"' -e 'config.platform="x86_64-unknown- mingw32"' -e 'config.os="mingw32"' -e 'config.arch="x86_64"' -e 'config.wordsize="64"' -e 'config.timeout=int() or config.timeout' -e 'config.exeext=".exe"' -e 'config.top="/home/drydock/ghc/testsuite"' --config 'compiler="/home/drydock/ghc/inplace/bin/ghc-stage1.exe"' --config 'ghc_pkg="/home/drydock/ghc/inplace/bin/ghc-pkg.exe"' --config 'haddock="/home/drydock/ghc/inplace/bin/haddock.exe"' --config 'hp2ps="/home/drydock/ghc/inplace/bin/hp2ps.exe"' --config 'hpc="/home/drydock/ghc/inplace/bin/hpc.exe"' --config 'gs="gs"' --config 'timeout_prog="../../timeout/install-inplace/bin/timeout.exe"' -e "config.stage=1" --summary-file "../../../testsuite_summary_stage1.txt" --no-print-summary 1 \ \ \ \ \ \ \ Warning: Ignoring request to use threads as running on Windows Traceback (most recent call last): File "../../driver/runtests.py", line 174, in <module> if mydll.kernel32.SetConsoleCP(65001) == 0: File "/usr/lib/python2.7/ctypes/__init__.py", line 435, in __getattr__ dll = self._dlltype(name) File "/usr/lib/python2.7/ctypes/__init__.py", line 365, in __init__ self._handle = _dlopen(self._name, mode) OSError: No such file or directory }}} From the repl it indeed seems that `ctypes.cdll.kernel32` is broken, {{{ $ python >>> import ctypes >>> ctypes.cdll.kernel32 Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python3.4/ctypes/__init__.py", line 421, in __getattr__ dll = self._dlltype(name) File "/usr/lib/python3.4/ctypes/__init__.py", line 351, in __init__ self._handle = _dlopen(self._name, mode) OSError: No such file or directory }}} Tamar, do you have any idea what is going on here? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12661> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11748: GHC runtime linker: fatal error: I found a duplicate definition for symbol
by GHC 27 Jan '17

27 Jan '17

#11748: GHC runtime linker: fatal error: I found a duplicate definition for symbol -------------------------------------+------------------------------------- Reporter: jeiea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 (Linking) | Keywords: | Operating System: Windows Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I found GHC panic when using both inline-c and local Win32 package. I don't know whether it's related to #6107. {{{ D:\ghc-bug-maybe>stack build Win32a-2.3.1.0: build Win32a-2.3.1.0: copy/register ghc-bug-maybe-0.1.0.0: configure ghc-bug-maybe-0.1.0.0: build Completed 2 action(s). -- While building package ghc-bug-maybe-0.1.0.0 using: C:\AppData\Roaming\stack\setup-exe-cache\x86_64-windows\setup- Simple-Cabal-1.22.5.0-ghc-7.10.3.exe --builddir=.stack-work\dist\2672c1f3 build lib:ghc-bug-maybe exe:DualternativeH-exe --ghc-options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 Logs have been written to: D:\ghc-bug-maybe\.stack-work\logs\ghc-bug- maybe-0.1.0.0.log Configuring ghc-bug-maybe-0.1.0.0... Preprocessing library ghc-bug-maybe-0.1.0.0... [1 of 1] Compiling Lib ( src\Lib.hs, .stack- work\dist\2672c1f3\build\Lib.o ) GHC runtime linker: fatal error: I found a duplicate definition for symbol rgb whilst processing object file D:\ghc-bug-maybe\.stack-work\install\0464eb7a\lib\x86_64-windows- ghc-7.10.3\Win32a-2.3.1.0-JATTCAFziPX9UILXdwDTPA\HSWin32a-2.3.1.0-JATTCAFziPX9UILXdwDTPA.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. ghc.exe: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-mingw32): loadObj "D:\\ghc-bug-maybe\\.stack- work\\install\\0464eb7a\\lib\\x86_64-windows- ghc-7.10.3\\Win32a-2.3.1.0-JATTCAFziPX9UILXdwDTPA\\HSWin32a-2.3.1.0-JATTCAFziPX9UILXdwDTPA.o": failed Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11748> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9351: add ability to version symbols .c for packages with C code
by GHC 27 Jan '17

27 Jan '17

#9351: add ability to version symbols .c for packages with C code -------------------------------------+------------------------------------- Reporter: slyfox | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: backpack | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Let's consider an example: We have a haskell package with some C code imported in haskell: {{{ // a.h file int get_something(void); // a.c file #include "a.h" int get_something(void) { return 42; } // M.hs file module M where foreign import ccall "a.h get_something" :: IO Int }}} The problem here is we can't mix that package with other packages having global 'get_something' symbol. Sometimes it happens when a package copies part of implementation from another package with .c bits under different haskell namespace. Haskell parts would coexist freely, but not C symbols. Would be great if ghc would export some unique package identifier in a way C code could attach it to all exported symbols making linking possible. Something like that: {{{ // a.h file #include "HsFFI.h" /* #define FOR_HASKELL(__sym) package_id_##__sym */ int FOR_HASKELL(get_something)(void); // a.c file #include "a.h" int FOR_HASKELL(get_something)(void) { return 42; } // M.hs file module M where foreign import ccall-for-haskell "a.h get_something" :: IO Int }}} That way we explicitly mark symbol as inaccessible to external plain C code. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9351> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12805: Generalise type of asProxyTypeOf
by GHC 26 Jan '17

26 Jan '17

#12805: Generalise type of asProxyTypeOf -------------------------------------+------------------------------------- Reporter: tomjaguarpaw | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 8.0.1 libraries/base | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Could we please generalise the type of `asProxyTypeOf` to `asProxyTypeOf :: a -> proxy a -> a`? https://hackage.haskell.org/package/base-4.9.0.0/docs/Data- Proxy.html#v:asProxyTypeOf -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12805> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8901: (very) bad inline heuristics
by GHC 25 Jan '17

25 Jan '17

#8901: (very) bad inline heuristics ------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I observe a bad case for inlining blowup for the time library. Observed for 7.7, just checked in 7.9. The problem is so bad that the PowerPC32 assembler cannot resolve cross- routine references. (I have no error message at hand, but could try to get one.) Instead here are the stats for x86, with inlining and certain inlining suppressed. The architecture seems irrelevant. {{{ $ file ./libraries/time/dist-install/build/Data/Time/Format.o ./libraries/time/dist-install/build/Data/Time/Format.o: Mach-O object i386 $ ls -l ./libraries/time/dist-install/build/Data/Time/Format.* -rw-r--r-- 1 ggreif staff 61875 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.dyn_hi -rw-r--r-- 1 ggreif staff 450864 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.dyn_o -rw-r--r-- 1 ggreif staff 61863 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.hi -rw-r--r-- 1 ggreif staff 332216 Mar 15 16:48 ./libraries/time/dist- install/build/Data/Time/Format.o }}} With following patch applied: <https://github.com/ggreif/packages- time/commit/83f08b8896b950707a910fed4e30bddb7ee7f52f> I get: {{{ $ ls -l ./libraries/time/dist-install/build/Data/Time/Format.* -rw-r--r-- 1 ggreif staff 10554 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.dyn_hi -rw-r--r-- 1 ggreif staff 106832 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.dyn_o -rw-r--r-- 1 ggreif staff 10542 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.hi -rw-r--r-- 1 ggreif staff 78864 Mar 16 00:08 ./libraries/time/dist- install/build/Data/Time/Format.o }}} The factor is 4.2 for Format.o, Format.dyn_o and 5.8 for the .hi files. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8901> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12713: Bytes allocated statistic for T10858 differs between Windows and Linux
by GHC 25 Jan '17

25 Jan '17

#12713: Bytes allocated statistic for T10858 differs between Windows and Linux -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Test Suite | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Strangely `T10858` seems to pass without any trouble on 64-bit Linux with its current expected "bytes allocated" statistic of 241MB. Strangely, this test allocates 16% less on 64-bit Windows, {{{ bytes allocated value is too low: (If this is because you have improved GHC, please update the test so that GHC doesn't regress again) Expected T10858(normal) bytes allocated: 241655120 +/-8% Lower bound T10858(normal) bytes allocated: 222322710 Upper bound T10858(normal) bytes allocated: 260987530 Actual T10858(normal) bytes allocated: 203567896 Deviation T10858(normal) bytes allocated: -15.8 % *** unexpected stat test failure for T10858(normal) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12713> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12663: amazonka-ec2 fails to build with --split-objs
by GHC 24 Jan '17

24 Jan '17

#12663: amazonka-ec2 fails to build with --split-objs -------------------------------------+------------------------------------- Reporter: joehillen | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I've created a repo for reproducing this bug: https://github.com/joehillen/ec2-split-objs-bug The bug can appear as either: {{{ [189 of 207] Compiling Network.AWS.EC2.Waiters ( gen/Network/AWS/EC2/Waiters.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Network/AWS/EC2/Waiters.o ) [190 of 207] Compiling Network.AWS.EC2.DeleteVPNConnection ( gen/Network/AWS/EC2/DeleteVPNConnection.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Network/AWS/EC2/DeleteVPNConnection.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): tyThingTyCon Identifier ‘$fFoldableFirst_$cfold’ Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} or {{{ [189 of 207] Compiling Network.AWS.EC2.Waiters ( gen/Network/AWS/EC2/Waiters.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Network/AWS/EC2/Waiters.o ) [190 of 207] Compiling Network.AWS.EC2.DeleteVPNConnection ( gen/Network/AWS/EC2/DeleteVPNConnection.hs, .stack- work/dist/x86_64-linux/Cabal-1.24.0.0/build/Network/AWS/EC2/DeleteVPNConnection.o ) /tmp/stack11/amazonka- ec2-1.4.3/gen/Network/AWS/EC2/DeleteVPNConnection.hs:51:25: error: • Couldn't match expected type ‘Either a0 a10’ with actual type ‘a1 -> ShowS’ • Probable cause: ‘showsPrec’ is applied to too few arguments In the first argument of ‘GHC.Show.showList__’, namely ‘(showsPrec 0)’ In the expression: GHC.Show.showList__ (showsPrec 0) In an equation for ‘showList’: showList = GHC.Show.showList__ (showsPrec 0) When typechecking the code for ‘showList’ in a derived instance for ‘Show DeleteVPNConnection’: To see the code I am typechecking, use -ddump-deriv /tmp/stack11/amazonka- ec2-1.4.3/gen/Network/AWS/EC2/DeleteVPNConnection.hs:104:23: error: • Couldn't match expected type ‘Either a2 a3’ with actual type ‘a4 -> ShowS’ • Probable cause: ‘showsPrec’ is applied to too few arguments In the first argument of ‘GHC.Show.showList__’, namely ‘(showsPrec 0)’ In the expression: GHC.Show.showList__ (showsPrec 0) In an equation for ‘showList’: showList = GHC.Show.showList__ (showsPrec 0) When typechecking the code for ‘showList’ in a derived instance for ‘Show DeleteVPNConnectionResponse’: To see the code I am typechecking, use -ddump-deriv }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12663> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8156: amd64 + in-tree gmp build broken
by GHC 23 Jan '17

23 Jan '17

#8156: amd64 + in-tree gmp build broken -------------------------------------+------------------------------------- Reporter: errge | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Build System | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 (amd64) | Type of failure: Building GHC Difficulty: Easy (less than 1 | failed hour) | Test Case: Blocked By: | Blocking: Related Tickets: #4022 #4366 #4374 | -------------------------------------+------------------------------------- Currently, the GHC build system has an in-tree GMP. This GMP seems to be used only if there is no usable GMP found on the system and the user didn't provide one using configure flags. When we build GHC using an external shared version of GMP, the resulting GHC is dynamically linked against GMP and also the generated programs are linked dynamically against GMP. When the in-tree GMP is used, it is built statically, even if the GHC we are building is shared GHC on GNU/Linux. This feature is currently broken on amd64 (#4366, #4022), but is working currently very well on Linux i686. Apart from the breakage this setting is very flexible and I'd be very happy if it were possible to keep it, in spite of removeal requests like #4374. When there is a system GMP, nothing would change, this is the most typical usage, e.g. distributions are all building this way. On the other hand, if the user removes his GMP (maybe we should provide an option to explicity trigger this in ./configure, instead of having to remove GMP); she can build a GHC that is not linked dynamically against GMP and the resulting programs are not linked either. This makes it possible to generate binaries that link dynamically against libc (no -static) which is quite compatible amongst versions, but doesn't require a libgmp.so to run. For binary deployments this seems to be the best kind of setup nowadays. Now, if we were only able to fix this for amd64. See this: https://www.gentoo.org/proj/en/base/amd64/howtos/index.xml?part=1&chap=3 On amd64 we can continue to compile GMP statically and link into the binary library, we just have to compile GMP with the fPIC. I attached the patch to fix this. Previously a similar patch has been rejected in #4022 because "this shouldn't be platform specific", but this is clearly not the case, this is specific to amd64. Tadaaaam: {{{ errge@sid64:~/ghc/inplace/bin$ cat test.hs main = print (2^100) errge@sid64:~/ghc/inplace/bin$ ./ghc-stage2 test.hs [1 of 1] Compiling Main ( test.hs, test.o ) Linking test ... errge@sid64:~/ghc/inplace/bin$ ./test 1267650600228229401496703205376 errge@sid64:~/ghc/inplace/bin$ ldd ./test linux-vdso.so.1 (0x00007fff79962000) libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fe4b9a83000) librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fe4b987a000) libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fe4b9676000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fe4b92c6000) libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fe4b90a6000) /lib64/ld-linux-x86-64.so.2 (0x00007fe4b9d83000) }}} No GMP! I attach the build file patch to the bugreport. So, can we please apply this patch and just keep the in-tree GMP? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8156> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12785: GHC panic, TypeFamily in equality constraint
by GHC 23 Jan '17

23 Jan '17

#12785: GHC panic, TypeFamily in equality constraint -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Compiling the attached module I get {{{ $ ghc --interactive Tree.hs GHCi, version 8.1.20161030: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Tree ( Tree.hs, interpreted ) Tree.hs:28:63: error:ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20161030 for x86_64-apple-darwin): tcTyVarDetails cobox0_a1eK :: (m_a1ej[sk:2] :: Peano) ~# ('S n_a1eJ[ssk:3] :: Peano) Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1076:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1080:37 in ghc:Outputable pprPanic, called at compiler/basicTypes/Var.hs:457:22 in ghc:Var Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} When switching the call to `SBranchX` in line 29 to a call to `SBranch` the program compiles. So I suspect that the problem is rooted in the extra constraint attached to constructor `SBranchX`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12785> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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