June 2015 - ghc-tickets

[GHC] #8613: simplifier ticks exhausted
by GHC 13 Jan '16

13 Jan '16

#8613: simplifier ticks exhausted ----------------------------------+---------------------------- Reporter: guest | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: MacOS X Architecture: x86_64 (amd64) | Type of failure: Other Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------------+---------------------------- (Sent by chrisreade(a)mac.com ) Compiler giving up with simplifier ticks exhausted. Large amount of simplification may be going on to cause this. The problem goes away when using -fsimpl-tick-factor=1000 and the code runs. This is the session output without the flag (asking to have bug reported): chris$ ghc -O2 -rtsopts RedBlackStencilOpt.hs -v Glasgow Haskell Compiler, Version 7.6.3, stage 2 booted by GHC version 7.4.2 Using binary package database: /Library/Frameworks/GHC.framework/Versions/7.6.3-x86_64/usr/lib/ghc-7.6.3/package.conf.d/package.cache Using binary package database: /Users/chris/.ghc/x86_64-darwin-7.6.3/package.conf.d/package.cache hiding package binary-0.5.1.1 to avoid conflict with later version binary-0.6.4.0 hiding package Cabal-1.16.0 to avoid conflict with later version Cabal-1.18.1.1 wired-in package ghc-prim mapped to ghc- prim-0.3.0.0-d5221a8c8a269b66ab9a07bdc23317dd wired-in package integer-gmp mapped to integer- gmp-0.5.0.0-2f15426f5b53fe4c6490832f9b20d8d7 wired-in package base mapped to base-4.6.0.1-6c351d70a24d3e96f315cba68f3acf57 wired-in package rts mapped to builtin_rts wired-in package template-haskell mapped to template- haskell-2.8.0.0-c2c1b21dbbb37ace4b7dc26c966ec664 wired-in package dph-seq not found. wired-in package dph-par not found. Hsc static flags: -static *** Chasing dependencies: Chasing modules from: *RedBlackStencilOpt.hs Stable obj: [] Stable BCO: [] Ready for upsweep [NONREC ModSummary { ms_hs_date = 2013-12-13 13:12:37 UTC ms_mod = main:RedBlackStencilOpt, ms_textual_imps = [import (implicit) Prelude, import Data.Array.Repa.Stencil.Dim2 as A, import Data.Array.Repa.Stencil as A, import Data.Array.Repa as A] ms_srcimps = [] }] *** Deleting temp files: Deleting: compile: input file RedBlackStencilOpt.hs Created temporary directory: /var/folders/dz/m1mks1yn1bsft72zgh105sw40000gn/T/ghc93155_0 *** Checking old interface for main:RedBlackStencilOpt: [1 of 1] Compiling RedBlackStencilOpt ( RedBlackStencilOpt.hs, RedBlackStencilOpt.o ) *** Parser: *** Renamer/typechecker: *** Simplify: *** CorePrep: *** ByteCodeGen: Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. *** gcc: '/usr/bin/gcc' '-m64' '-fno-stack-protector' '-m64' '-L/Library/Frameworks/GHC.framework/Versions/7.6.3-x86_64/usr/lib/ghc-7.6.3/base-4.6.0.1' '--print-file-name' 'libiconv.dylib' Loading package base ... linking ... done. Loading package pretty-1.1.1.0 ... linking ... done. Loading package array-0.4.0.1 ... linking ... done. Loading package deepseq-1.3.0.1 ... linking ... done. Loading package containers-0.5.0.0 ... linking ... done. Loading package old-locale-1.0.0.5 ... linking ... done. Loading package time-1.4.0.1 ... linking ... done. Loading package random-1.0.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package QuickCheck-2.6 ... linking ... done. Loading package bytestring-0.10.0.2 ... linking ... done. Loading package primitive-0.5.0.1 ... linking ... done. Loading package vector-0.10.0.1 ... linking ... done. Loading package repa-3.2.3.3 ... linking ... done. *** Simplify: *** CorePrep: *** ByteCodeGen: *** Desugar: Result size of Desugar (after optimization) = {terms: 900, types: 1,810, coercions: 340} *** Simplifier: Result size of Simplifier iteration=1 = {terms: 834, types: 1,757, coercions: 567} Result size of Simplifier iteration=2 = {terms: 830, types: 1,721, coercions: 567} Result size of Simplifier = {terms: 830, types: 1,721, coercions: 567} *** Specialise: Result size of Specialise = {terms: 830, types: 1,721, coercions: 567} *** Float out(FOS {Lam = Just 0, Consts = True, PAPs = False}): Result size of Float out(FOS {Lam = Just 0, Consts = True, PAPs = False}) = {terms: 993, types: 2,131, coercions: 567} *** Float inwards: Result size of Float inwards = {terms: 993, types: 2,131, coercions: 567} *** Simplifier: *** Deleting temp files: Deleting: /var/folders/dz/m1mks1yn1bsft72zgh105sw40000gn/T/ghc93155_0/ghc93155_0.s Warning: deleting non-existent /var/folders/dz/m1mks1yn1bsft72zgh105sw40000gn/T/ghc93155_0/ghc93155_0.s *** Deleting temp dirs: Deleting: /var/folders/dz/m1mks1yn1bsft72zgh105sw40000gn/T/ghc93155_0 ghc: panic! (the 'impossible' happened) (GHC version 7.6.3 for x86_64-apple-darwin): Simplifier ticks exhausted When trying RuleFired Class op szipWith To increase the limit, use -fsimpl-tick-factor=N (default 100) If you need to do this, let GHC HQ know, and what factor you needed To see detailed counts use -ddump-simpl-stats Total ticks: 60402 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8613> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10070: Cross compiling from Linux to Windows with mising Win32 library
by GHC 13 Jan '16

13 Jan '16

#10070: Cross compiling from Linux to Windows with mising Win32 library -------------------------------------+------------------------------------- Reporter: erikd | Owner: erikd Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: Build | Version: 7.11 System | Operating System: Unknown/Multiple Keywords: cross- | Type of failure: Building GHC compiling | failed Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- After applying the proposed patch from #9524, building a Linux to Windows cross-compiler terminates with: {{{ Configuring time-1.5.0.1... ghc-cabal: At least the following dependencies are missing: Win32 -any }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10070> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9048: armel: evacuate(static): strange closure type 0
by GHC 13 Jan '16

13 Jan '16

#9048: armel: evacuate(static): strange closure type 0 ------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I guess I need to document the build failures here, instead of just mentioning them on the mailing list: Building 7.8 on armel on Debian fails with {{{ chmod +x inplace/bin/runghc inplace/bin/dll-split compiler/stage2/build/.depend-v-p-dyn.haskell "DynFlags" "Annotations Avail Bag BasicTypes BinIface Binary Bitmap BlockId BooleanFormula BreakArray BufWrite BuildTyCl ByteCodeAsm ByteCodeInstr ByteCodeItbls CLabel Class CmdLineParser Cmm CmmCallConv CmmExpr CmmInfo CmmMachOp CmmNode CmmType CmmUtils CoAxiom ConLike CodeGen.Platform CodeGen.Platform.ARM CodeGen.Platform.NoRegs CodeGen.Platform.PPC CodeGen.Platform.PPC_Darwin CodeGen.Platform.SPARC CodeGen.Platform.X86 CodeGen.Platform.X86_64 Coercion Config Constants CoreArity CoreFVs CoreLint CoreSubst CoreSyn CoreTidy CoreUnfold CoreUtils CostCentre DataCon Demand Digraph DriverPhases DsMonad DynFlags Encoding ErrUtils Exception ExtsCompat46 FamInstEnv FastBool FastFunctions FastMutInt FastString FastTypes Finder Fingerprint FiniteMap ForeignCall Hooks Hoopl Hoopl.Dataflow HsBinds HsDecls HsDoc HsExpr HsImpExp HsLit HsPat HsSyn HsTypes HsUtils HscTypes IOEnv Id IdInfo IfaceEnv IfaceSyn IfaceType InstEnv InteractiveEvalTypes Kind ListSetOps Literal LoadIface Maybes MkCore MkGraph MkId Module MonadUtils Name NameEnv NameSet OccName OccurAnal OptCoercion OrdList Outputable PackageConfig Packages Pair Panic PatSyn PipelineMonad Platform PlatformConstants PprCmm PprCmmDecl PprCmmExpr PprCore PrelInfo PrelNames PrelRules Pretty PrimOp RdrName Reg RegClass Rules SMRep Serialized SrcLoc StaticFlags StgCmmArgRep StgCmmClosure StgCmmEnv StgCmmLayout StgCmmMonad StgCmmProf StgCmmTicky StgCmmUtils StgSyn Stream StringBuffer TcEvidence TcIface TcRnMonad TcRnTypes TcType TcTypeNats TrieMap TyCon Type TypeRep TysPrim TysWiredIn Unify UniqFM UniqSet UniqSupply Unique Util Var VarEnv VarSet" dll-split: internal error: evacuate(static): strange closure type 0 (GHC version 7.8.2 for arm_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug make[2]: *** [compiler/stage2/dll-split.stamp] Aborted make[2]: *** Waiting for unfinished jobs.... make[1]: *** [all] Error 2 }}} Unfortunately, I’m no expert in strange architectures, so I need help from all you arm-lovers out there... Can someone, for starters, confirm this on an arm machine, or is this Debian specific somehow? (Hardening flags have been disabled.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9048> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10476: Wrong ar during cross-compilation
by GHC 10 Jan '16

10 Jan '16

#10476: Wrong ar during cross-compilation -------------------------------------+------------------------------------- Reporter: jakzale | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Build | Version: 7.11 System | Operating System: Unknown/Multiple Keywords: cross- | Type of failure: Building GHC compiling | failed Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- It appears that during cross-compilation, while building stage 1 ghc, the build system uses ar for target architecture instead of ar for build/host architecture. It will cause linking errors on systems where ar for target architecture is incompatible with ar for build/host architecture (sample output attached below). {{{ (...) "rm" -f libraries/Cabal/Cabal/dist- boot/build/libHSCabal-1.22.3.0-3tdTeip89ooLNDDdwdA54s.a.contents "rm" -f libraries/bin-package-db/dist-boot/build/libHSbin-package- db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a libraries/bin-package-db/dist- boot/build/libHSbin-package-db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a.contents echo libraries/bin-package-db/dist-boot/build/GHC/PackageDb.o >> libraries/bin-package-db/dist-boot/build/libHSbin-package- db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a.contents "/Users/jakub/src/haskell/PNaCl/gsoc/wrappers/i686-unknown-nacl-ar" q libraries/bin-package-db/dist-boot/build/libHSbin-package- db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a @libraries/bin-package-db/dist- boot/build/libHSbin-package-db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a.contents /Users/jakub/src/nacl_sdk/pepper_canary/toolchain/mac_x86_newlib/bin/i686 -nacl-ar: creating libraries/bin-package-db/dist-boot/build/libHSbin- package-db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a "rm" -f libraries/bin-package-db/dist-boot/build/libHSbin-package- db-0.0.0.0-Gk3F1vzzO3g80wuNGtok3x.a.contents (...) ld: archive has no table of contents file '/Users/jakub/src/haskell/PNaCl /ghc-pnacl/libraries/terminfo/dist- boot/build/libHSterminfo-0.4.0.1-7qZwBlx3clR8sTBilJl253.a' for architecture x86_64 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10476> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10273: haskeline : Cross-compile from Linux to Windows fails due to <Shlobj.h>
by GHC 09 Jan '16

09 Jan '16

#10273: haskeline : Cross-compile from Linux to Windows fails due to <Shlobj.h> -------------------------------------+------------------------------------- Reporter: erikd | Owner: erikd Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: libraries | Version: 7.11 (other) | Operating System: Unknown/Multiple Keywords: | Type of failure: Building GHC Architecture: | failed Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #10070 Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The #include of <Shlobj.h> doesn't work when cross-compiling from Linux to Windows because the Linux file system is case sensitive and on Linux the file is <shlobj.h>. Down casing the name of this include file should not cause problems on Windows as the Windows file system is case insensitive. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10273> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8736: GHCi doesn't load .dyn_o files appropriately
by GHC 09 Jan '16

09 Jan '16

#8736: GHCi doesn't load .dyn_o files appropriately ------------------------------------+------------------------------------- Reporter: thoughtpolice | Owner: thoughtpolice Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.8.1-rc1 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Now that GHCi generally defaults to dynamic linking, it handles dynamic object files. But it doesn't implicitly handle the `-dynamic-too` case appropriately: {{{ $ cat Test.hs main = return () $ ./inplace/bin/ghc-stage2 -dynamic Test.hs [1 of 1] Compiling Main ( Test.hs, Test.o ) Linking Test ... $ ./inplace/bin/ghc-stage2 --interactive Test GHCi, version 7.8.20140130: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Ok, modules loaded: Main. Prelude Main> ^D $ ./inplace/bin/ghc-stage2 -dynamic-too Test.hs [1 of 1] Compiling Main ( Test.hs, Test.o ) Linking Test ... $ ./inplace/bin/ghc-stage2 --interactive Test GHCi, version 7.8.20140130: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( Test.hs, interpreted ) Ok, modules loaded: Main. *Main> }}} Also: {{{ $ ./inplace/bin/ghc-stage2 --interactive Test.dyn_o GHCi, version 7.8.20140130: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Warning: ignoring unrecognised input `Test.dyn_o' Prelude> }}} but it does handle the `.o` case. This should all be fixed and merged to 7.8 since it'll likely be very annoying. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8736> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8793: Improve GHC.Event.IntTable performance
by GHC 09 Jan '16

09 Jan '16

#8793: Improve GHC.Event.IntTable performance ------------------------------------+------------------------------------- Reporter: cdk | Owner: Type: task | Status: new Priority: normal | Milestone: 7.8.1 Component: libraries/base | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- The performance of `GHC.Event.IntTable` can be improved. I've managed to get some nice increases across the board. Benchmarking using `criterion` shows: function, % faster than current impl. `insert`: 4% `lookup`: 26% `update`: 11% `delete`: 5% There is one strange thing I noted. In `updateWith`, there is an inner loop that looks like this: {{{ data Bucket a = Empty | Bucket Int a (Bucket a) go _ Empty = (False, Nothing, Empty) go cont (Bucket key val next) | key == k = case f val of Nothing -> (True, Just val, cont next) Just v -> (False, Just val, cont (Bucket key v next)) | otherwise = go (\x -> cont (Bucket key val x)) next }}} which returns a tuple that is immediately consumed like so: {{{ (delete_occurred, old_val, new_bkt) <- go id ... when (isJust old_val) $ do <updateIntTable> when delete_occurred <decIntTableSize> return old_val }}} I expected that inlining the `<updateIntTable>` and `<decIntTableSize>` code blocks directly into `go` would result in better code than creating a tuple and then pattern matching on it afterwards. ie. {{{ go _ Empty = return Nothing go cont (Bucket key val next) | key == k = do case f val of Nothing -> <updateIntTable> (cont next) >> <decIntTableSize> Just v -> <updateIntTable> (cont (Bucket key v next) return (Just val) | otherwise = go (\x -> cont (Bucket key val x)) next }}} which has the exact same semantics. To my suprise, this code is almost 2x slower! The core generated in both cases is exactly what I'd expect; if anything, the second version seems tighter. I'm not sure why the first version is faster, but perhaps the original author, Bryan O'Sullivan, can shed some light as he used the tupled method in the first version. I'll attach my patch, `criterion`'s html output for the benchmarks as well as the benchmarking code, and the core for the oddity I discussed above. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8793> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10337: One-shot module loops have hard to understand messages
by GHC 09 Jan '16

09 Jan '16

#10337: One-shot module loops have hard to understand messages -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | 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: | -------------------------------------+------------------------------------- Consider these two modules: {{{ -- A.hs module A where -- B.hs module B where import A }}} `ghc --make B.hs` will compile this fine. Now edit `A.hs` to be circular: {{{ -- A.hs module A where import B }}} and attempt to one-shot compile it with `ghc -c A.hs`. You will now get an uninformative error message: {{{ A.hs:1:1: Circular imports: module `A' depends on itself }}} You can get a more informative message with `--make`: {{{ Module imports form a cycle: module `A' (A.hs) imports `B' (./B.hs) which imports `A' (A.hs) }}} We should either suggest users try again with `--make`, or try harder to give a useful message in one-shot mode. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10337> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10362: Make tuple constraints into a class
by GHC 09 Jan '16

09 Jan '16

#10362: Make tuple constraints into a class -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- At the moment GHC treats tuple constraints specially. If you grep for `TuplePred` you'll see this. But the special treatment is strange; see the confusion between constraint tuples and ordinary tuples in #9858. But I now realise that we can sweep away all this nonsense. Suppose we declare {{{ module GHC.Classes where class (c1, c2) => (,) c1 c2 instance (c1, c2) => (,) c1 c2 class (c1, c2, c3) => (,) c1 c2 c3 instance (c1, c2, c3) => (,) c1 c2 c3 }}} and so on. (This is analogous the tuple data type declarations in `GHC.Tuple`.) Notice that: * `GHC.Classes,(,)` is a class, of kind `Constraint -> Constraint -> Constraint`. quite distinct from `GHC.Tuple.(,)`, whose kind is `* -> * -> *`. * `GHC.Classes.(,)` is a perfectly ordinary class, with no methods and two superclasses. * So all the usual superclass stuff applies. * If you have a given `Ord a` then you have a given `Eq a` (its superclass). Similarly if you have a given `(,) c1 c2` then you also have given `c1` and `given `c2`. * If you want to construct a dictionary of type `Ord a` (a "wanted"), you must supply a dictionary of type `Eq a`. Similarly, if you want to construct a dictionary of type `(,) c1 c2` then you must supply `c1` and `c2`. * I have written `(,) c1 c2` to stress that there is a class `GHC.Classes.(,)`, but we'll also allow the concrete syntax `(c1,c2)` instead. * Nevertheless the syntactic form `(c1, c2) => blah` is just sugar for `c1 => c2 => blah` (a type with two, curried constraints); it does not stand a type with a single constraint. Otherwise the instance {{{ instance (c1,c2) => (c1,c2) }}} would be the identity function! The key thing is that, aside from special syntax, `(,)` is a perfectly ordinary class, so we can simply delete all the special treatment of `TuplePred`. (Implicit parameters are also treated as a special class, incidentally.) There should be no user-visible effects. But I think it would cure the worst aspects of #10359, as well as cleaning up `TypeRep` confusion. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10362> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9009: Confusing error message when loading package with TH
by GHC 08 Jan '16

08 Jan '16

#9009: Confusing error message when loading package with TH ------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Package system | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Other Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I got this error message when compiling a file that calls Template Haskell function from `singletons` package: {{{ [1 of 1] Compiling Splices ( Splices.hs, Splices.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package transformers-0.3.0.0 ... linking ... done. Loading package pretty-1.1.1.1 ... linking ... done. Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. Loading package mtl-2.1.2 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package syb-0.4.1 ... linking ... done. Loading package th-desugar-1.4.0 ... linking ... done. Loading package singletons-1.0 ... <command line>: can't load .so/.DLL for: /home/killy/.cabal/lib/x86_64-linux- ghc-7.8.2/singletons-1.0/libHSsingletons-1.0-ghc7.8.2.so (/home/killy/.cabal/lib/x86_64-linux- ghc-7.8.2/singletons-1.0/libHSsingletons-1.0-ghc7.8.2.so: undefined symbol: singletonszm1zi0_DataziSingletonsziSingleziMonad_lookupProxy1_info) }}} After some investigation it turned out that the module Data.Singletons.Single.Monad was not listed in singletons.cabal file - neither under exported-modules nor other-modules - when the package was installed. The error message is mostly confusing. It would be good to at least get a hint on the possible cause. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9009> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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