August 2011 - Glasgow-haskell-users

ghc-pkg unregister disobedience
by Albert Y. C. Lai 30 Aug '11

30 Aug '11

For package P, "ghc-pkg unregister --user P" drops the global package if P is not in user. "ghc-pkg unregister --global P" drops the user package if P is in user. "ghc-pkg unregister --package-conf=<dir> P" drops the user or the global package, preferring the user one, if P is not found in <dir>. Same with "ghc-pkg --user unregister P", "ghc-pkg unregister P --user", etc. GHC versions 6.10, 6.12, 7.0, 7.2.

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Bug in GC's ordering of ForeignPtr finalization?
by Ben Gamari 29 Aug '11

29 Aug '11

On Tue, 16 Aug 2011 12:32:13 -0400, Ben Gamari <bgamari.foss(a)gmail.com> wrote: > It seems that the notmuch-haskell bindings (version 0.2.2 built against > notmuch from git master; passes notmuch-test) aren't dealing with memory > management properly. In particular, the attached test code[1] causes > talloc to abort. Unfortunately, while the issue is consistently > reproducible, it only occurs with some queries (see source[1]). I have > been unable to establish the exact criterion for failure. > > It seems that the crash is caused by an invalid access to a freed Query > object while freeing a Messages object (see Valgrind trace[3]). I've > taken a brief look at the bindings themselves but, being only minimally > familiar with the FFI, there's nothing obviously wrong (the finalizers > passed to newForeignPtr look sane). I was under the impression that > talloc was reference counted, so the Query object shouldn't have been > freed unless if there was still a Messages object holding a > reference. Any idea what might have gone wrong here? Thanks! > After looking into this issue in a bit more depth, I'm even more confused. In fact, I would not be surprised if I have stumbled into a bug in the GC. It seems that the notmuch-haskell bindings follow the example of the python bindings in that child objects keep references to their parents to prevent the garbage collector from releasing the parent, which would in turn cause talloc to free the child objects, resulting in odd behavior when the child objects were next accessed. For instance, the Query and Messages objects are defined as follows, type MessagesPtr = ForeignPtr S__notmuch_messages type MessagePtr = ForeignPtr S__notmuch_message newtype Query = Query (ForeignPtr S__notmuch_query) data MessagesRef = QueryMessages { qmpp :: Query, msp :: MessagesPtr } | ThreadMessages { tmpp :: Thread, msp :: MessagesPtr } | MessageMessages { mmspp :: Message, msp :: MessagesPtr } data Message = MessagesMessage { msmpp :: MessagesRef, mp :: MessagePtr } | Message { mp :: MessagePtr } type Messages = [Message] As seen in the Valgrind dump given in my previous message, it seems that the Query object is being freed before the Messages object. Since the Messages object is a child of the Query object, this fails. In my case, I'm calling queryMessages which begins by issuing a given notmuch Query, resulting in a MessagesPtr. This is then packaged into a QueryMessages object which is then passed off to unpackMessages. unpackMessages iterates over this collection, creating MessagesMessage objects which themselves refer to the QueryMessages object. Finally, these MessagesMessage objects are packed into a list, resulting in a Messages object. Thus we have the following chain of references, MessagesMessage | | msmpp \/ QueryMessages | | qmpp \/ Query As we can see, each MessagesMessage object in the Messages list resulting from queryMessages holds a reference to the Query object from which it originated. For this reason, I fail to see how it is possible that the RTS would attempt to free the Query before freeing the MessagesPtr. Did I miss something in my analysis? Are there tools for debugging issues such as this? Perhaps this is a bug in the GC? Any help at all would be greatly appreciated. Cheers, - Ben

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Prototype of 'docase' notation
by Tomas Petricek 26 Aug '11

26 Aug '11

Hello,! at the Cambridge Hackathon, I started implementing an extension for GHC that adds the 'docase' notation. The notation is a syntactic sugar that can makes it easier to write code that works with monads that have three additional operations (parallel composition, choice and aliasing). Such monads include various moands for parallel and concurrent programming (Par monad, CPH and Orc) as well as other monads such as parsers. The proposal is in details discussed in our Haskell Symposium paper: http://www.cl.cam.ac.uk/~tp322/papers/docase.html (the page also contains link to earlier pre-processor based prototype with a couple of more examples). I created a GHC Trac ticket to track the discussion about the feature: http://hackage.haskell.org/trac/ghc/ticket/5429. A prototype version of the GHC extension is available here: http://github.com/tpetricek/Haskell.Extensions/commits/. I'd love to hear some feedback about the feature and the extension: * Do you think this is a useful extension and do you know about any monads that could benefit from it? * What is the best syntax for the feature? (The notation intentionally resembles 'case' pattern matching, but there are some differences) * The feature adds some aspects of recently added monad comprehensions using do-style syntax, but both 'docase' and monad comprehensions have features that cannot be written using the other. Is that a good desing, or should there be a closer correspondence? * Can anybody review the prototype implementation? (I believe it is a reasonably modular change, so it should not affect the rest of the language, but is there anything missing/incorrect?) Thanks! Tomas

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With every new GHC release, also released any new versions of libraries
by Johan Tibell 26 Aug '11

26 Aug '11

Hi! As part of GHC releases users also get a bunch of libraries. These libraries (e.g. array-0.3.0.3 in the last release) aren't uploaded on Hackage. This has some problems, including users on older versions of GHC not being able to upgrade to the new versions and broken documentation on Hackage. I suggest that with each GHC release the new library releases should be uploaded to Hackage. Also, for libraries not maintained by GHC but shipped with the compiler (e.g. containers) the new releases should be done by the maintainers of those libraries to make sure no half-finished code gets shipped (i.e. the repo might not be in a good state to release at all times). P.S. Could someone please remind me why containers ships with GHC? Cheers, Johan

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building GHC on a cluster
by Karel Gardas 25 Aug '11

25 Aug '11

Hello, recent "GHC build times on newer MacBook Pros?" thread makes me wondering if someone already attempted to build GHC on a cluster of machines using for example PVM GNU make[1] for this or any other tool ( or even custom generated bin/ghc-stageX scripts using rsh?) which is suitable for the task. I'm asking since build of GHC HEAD on my ARM/Linux (OMAP4 1GHz) using both cores takes around 7 hours and yet buying another 3 machines might be well in the finance envelope of hobby project and speed the development which usually happens only during weekend's evenings... Thanks! Karel [1]: http://pvmgmake.sourceforge.net/

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Cheap and cheerful partial evaluation
by Edward Z. Yang 24 Aug '11

24 Aug '11

Hello all, It occurred to me that it might not be too difficult to use GHC's optimization passes as a cheap and cheerful partial evaluator. Consider some function we would like to partially evaluate: f = g h Partial evaluation proceeds as follows: calculate the type of f, inline and specialize g, inline and specialize h, and then optimize. Effectively, laser-guided inlining. With this (very) heavy hammer, we can, for example, solve the problem posed in http://hackage.haskell.org/trac/ghc/ticket/1349, simply by ensuring all of our "strict functions" are partially evaluated on the continuation handler appropriately. (This is not ideal, since we ought to be able to share the strict worker/wrapper between instances, but might be a reasonable stop-gap for some use cases.) So, am I completely insane, or does this seem plausible and easy enough to implement to make it into GHC? Cheers, Edward

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alternative to loadWithLogge
by Kazu Yamamoto 24 Aug '11

24 Aug '11

Hello, ghc-mod, IDE-like back-end for Emacs, uses warning related APIs including loadWithLogger and getWarnings in GHC 7.0.3 API. I found that they disappeared in GHC 7.2.1 API. What should I use to handle warnings in GHC 7.2.1 API? --Kazu

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What are the preconditions of newArray#
by Johan Tibell 23 Aug '11

23 Aug '11

Hi, I'm seeing a segfault which I suspect is due to allocating Array#s of size 0, using newArray#. Are zero length arrays allowed? What are the preconditions of newArray#? It'd be great if they were documented. -- Johan

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Where is stg_eqWord32 defined?
by Johan Tibell 23 Aug '11

23 Aug '11

Hi, I'm trying to add a method to Data.Bits, which requires that I implement versions for 16 and 32-bit platforms. I was trying to find some examples to model my code on and randomly picked (==) for Word32. (==) for Word32 is implemented in terms of stg_eqWord32, but I cannot find that function defined anywhere. I assume it's generated somehow. Where should I look? Cheers, Johan

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Can't find interface-file declaration for type constructor or class integer-gmp:GHC.Integer.Type.Integer
by Johan Tibell 19 Aug '11

19 Aug '11

I'm trying to refactor the integer-gmp package to fix the breakage explained in #5384. During the refactoring I * moved GHC.Integer.Type to GHC.Integer.GMP.Type, and * added a new GHC.Integer.Type module that re-exports parts of the interface now exposed by GHC.Integer.GMP.Type The content of GHC.Integer.Type is just: {-# LANGUAGE NoImplicitPrelude #-} {-# OPTIONS_HADDOCK hide #-} -- If you change the module name or the export list you must update -- compiler/prelude/PrelNames.lhs. module GHC.Integer.Type ( Integer(..) , plusInteger , timesInteger , smallInteger , integerToWord , integerToInt , minusInteger , negateInteger , eqInteger , neqInteger , absInteger , signumInteger , leInteger , gtInteger , ltInteger , geInteger , compareInteger , gcdInteger , lcmInteger , andInteger , orInteger , xorInteger , complementInteger , shiftLInteger , shiftRInteger ) where import GHC.Integer.GMP.Type GHC doesn't seem to like this at all. It can no longer find the GHC.Integer.Type.Integer type: $ "inplace/bin/ghc-stage1" -H64m -O -fasm -package-name base-4.4.0.0 -hide-all-packages -i -ilibraries/base/. -ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/autogen -Ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build/autogen -Ilibraries/base/include -optP-DOPTIMISE_INTEGER_GCD_LCM -optP-include -optPlibraries/base/dist-install/build/autogen/cabal_macros.h -package ghc-prim-0.2.0.0 -package integer-gmp-0.3.0.0 -package rts-1.0 -package-name base -XHaskell98 -XCPP -O -dcore-lint -no-user-package-conf -rtsopts -odir libraries/base/dist-install/build -hidir libraries/base/dist-install/build -stubdir libraries/base/dist-install/build -hisuf hi -osuf o -hcsuf hc -c libraries/base/./Data/Maybe.hs -o libraries/base/dist-install/build/Data/Maybe.o libraries/base/Data/Maybe.hs:70:13: Can't find interface-file declaration for type constructor or class integer-gmp:GHC.Integer.Type.Integer Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error When deriving the instance for (Eq (Maybe a)) Here's the -ddump-if-trace log: $ "inplace/bin/ghc-stage1" -H64m -O -fasm -package-name base-4.4.0.0 -hide-all-packages -i -ilibraries/base/. -ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/autogen -Ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build/autogen -Ilibraries/base/include -optP-DOPTIMISE_INTEGER_GCD_LCM -optP-include -optPlibraries/base/dist-install/build/autogen/cabal_macros.h -package ghc-prim-0.2.0.0 -package integer-gmp-0.3.0.0 -package rts-1.0 -package-name base -XHaskell98 -XCPP -O -dcore-lint -no-user-package-conf -rtsopts -odir libraries/base/dist-install/build -hidir libraries/base/dist-install/build -stubdir libraries/base/dist-install/build -hisuf hi -osuf o -hcsuf hc -c libraries/base/./Data/Maybe.hs -o libraries/base/dist-install/build/Data/Maybe.o -ddump-if-trace FYI: cannont read old interface file: libraries/base/dist-install/build/Data/Maybe.hi: openBinaryFile: does not exist (No such file or directory) Considering whether to load base:GHC.Base Reading interface for base:GHC.Base; reason: GHC.Base is directly imported readIFace libraries/base/dist-install/build/GHC/Base.hi updating EPS_ Considering whether to load ghc-prim:GHC.Generics Reading interface for ghc-prim:GHC.Generics; reason: GHC.Generics is directly imported readIFace /usr/local/google/src/ghc/libraries/ghc-prim/dist-install/build/GHC/Generics.hi updating EPS_ updating EPS_ Considering whether to load base:GHC.Base {- SYSTEM -} loadHiBootInterface base:Data.Maybe Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Reading interface for ghc-prim:GHC.Types; reason: Checking fixity for : readIFace /usr/local/google/src/ghc/libraries/ghc-prim/dist-install/build/GHC/Types.hi updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Starting fork { Declaration for Monad Loading decl for GHC.Base.Monad updating EPS_ buildClass buildClass GHC.Base.T:Monad } ending fork Declaration for Monad Starting fork { Declaration for Functor Loading decl for GHC.Base.Functor updating EPS_ buildClass buildClass GHC.Base.T:Functor } ending fork Declaration for Functor tcImportDecl GHC.Classes.Eq Need decl for GHC.Classes.Eq Considering whether to load ghc-prim:GHC.Classes {- SYSTEM -} Reading interface for ghc-prim:GHC.Classes; reason: Need decl for GHC.Classes.Eq readIFace /usr/local/google/src/ghc/libraries/ghc-prim/dist-install/build/GHC/Classes.hi updating EPS_ Starting fork { Declaration for Eq Loading decl for GHC.Classes.Eq updating EPS_ buildClass buildClass GHC.Classes.T:Eq } ending fork Declaration for Eq Starting fork { Declaration for Ord Loading decl for GHC.Classes.Ord updating EPS_ buildClass buildClass GHC.Classes.T:Ord } ending fork Declaration for Ord Starting fork { Declaration for Generic Loading decl for GHC.Generics.Generic updating EPS_ buildClass buildClass GHC.Generics.T:Generic } ending fork Declaration for Generic Starting fork { Declaration for D1 Loading decl for GHC.Generics.D1 updating EPS_ } ending fork Declaration for D1 Starting fork { Declaration for C1 Loading decl for GHC.Generics.C1 updating EPS_ } ending fork Declaration for C1 Starting fork { Declaration for S1 Loading decl for GHC.Generics.S1 updating EPS_ } ending fork Declaration for S1 Starting fork { Declaration for NoSelector Loading decl for GHC.Generics.NoSelector updating EPS_ tcIfaceDecl4 GHC.Generics.NoSelector } ending fork Declaration for NoSelector Starting fork { Declaration for Rec0 Loading decl for GHC.Generics.Rec0 updating EPS_ } ending fork Declaration for Rec0 Starting fork { Declaration for Par0 Loading decl for GHC.Generics.Par0 updating EPS_ } ending fork Declaration for Par0 Starting fork { Declaration for U1 Loading decl for GHC.Generics.U1 updating EPS_ tcIfaceDecl4 GHC.Generics.U1 } ending fork Declaration for U1 Starting fork { Declaration for V1 Loading decl for GHC.Generics.V1 updating EPS_ tcIfaceDecl4 GHC.Generics.V1 } ending fork Declaration for V1 Starting fork { Declaration for :+: Loading decl for GHC.Generics.:+: updating EPS_ tcIfaceDecl4 GHC.Generics.:+: } ending fork Declaration for :+: Starting fork { Declaration for :*: Loading decl for GHC.Generics.:*: updating EPS_ tcIfaceDecl4 GHC.Generics.:*: } ending fork Declaration for :*: Starting fork { Declaration for Datatype Loading decl for GHC.Generics.Datatype updating EPS_ buildClass buildClass GHC.Generics.T:Datatype } ending fork Declaration for Datatype Starting fork { Declaration for Constructor Loading decl for GHC.Generics.Constructor updating EPS_ buildClass buildClass GHC.Generics.T:Constructor } ending fork Declaration for Constructor Starting fork { Declaration for Selector Loading decl for GHC.Generics.Selector updating EPS_ buildClass mkNewTyConRhs GHC.Generics.NTCo:T:Selector buildClass GHC.Generics.T:Selector } ending fork Declaration for Selector Starting fork { Dict fun GHC.Classes.$fEq[] Starting fork { Declaration for $fEq[] Loading decl for GHC.Classes.$fEq[] updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} } ending fork Declaration for $fEq[] } ending fork Dict fun GHC.Classes.$fEq[] Starting fork { Dict fun GHC.Classes.$fEqOrdering Starting fork { Declaration for $fEqOrdering Loading decl for GHC.Classes.$fEqOrdering updating EPS_ Need decl for GHC.Ordering.Ordering Considering whether to load ghc-prim:GHC.Ordering {- SYSTEM -} Reading interface for ghc-prim:GHC.Ordering; reason: Need decl for GHC.Ordering.Ordering readIFace /usr/local/google/src/ghc/libraries/ghc-prim/dist-install/build/GHC/Ordering.hi updating EPS_ } ending fork Declaration for $fEqOrdering } ending fork Dict fun GHC.Classes.$fEqOrdering Starting fork { Declaration for Ordering Loading decl for GHC.Ordering.Ordering updating EPS_ tcIfaceDecl4 GHC.Ordering.Ordering } ending fork Declaration for Ordering Starting fork { Dict fun GHC.Classes.$fEqInt Starting fork { Declaration for $fEqInt Loading decl for GHC.Classes.$fEqInt updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} } ending fork Declaration for $fEqInt } ending fork Dict fun GHC.Classes.$fEqInt Starting fork { Dict fun GHC.Classes.$fEqFloat Starting fork { Declaration for $fEqFloat Loading decl for GHC.Classes.$fEqFloat updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} } ending fork Declaration for $fEqFloat } ending fork Dict fun GHC.Classes.$fEqFloat Starting fork { Dict fun GHC.Classes.$fEqFixity Starting fork { Declaration for $fEqFixity Loading decl for GHC.Classes.$fEqFixity updating EPS_ } ending fork Declaration for $fEqFixity } ending fork Dict fun GHC.Classes.$fEqFixity Starting fork { Declaration for Fixity Loading decl for GHC.Generics.Fixity updating EPS_ tcIfaceDecl4 GHC.Generics.Fixity } ending fork Declaration for Fixity Starting fork { Dict fun GHC.Classes.$fEqDouble Starting fork { Declaration for $fEqDouble Loading decl for GHC.Classes.$fEqDouble updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} } ending fork Declaration for $fEqDouble } ending fork Dict fun GHC.Classes.$fEqDouble Starting fork { Dict fun GHC.Classes.$fEqChar Starting fork { Declaration for $fEqChar Loading decl for GHC.Classes.$fEqChar updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} } ending fork Declaration for $fEqChar } ending fork Dict fun GHC.Classes.$fEqChar Starting fork { Dict fun GHC.Classes.$fEqBool Starting fork { Declaration for $fEqBool Loading decl for GHC.Classes.$fEqBool updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} } ending fork Declaration for $fEqBool } ending fork Dict fun GHC.Classes.$fEqBool Starting fork { Dict fun GHC.Classes.$fEqAssociativity Starting fork { Declaration for $fEqAssociativity Loading decl for GHC.Classes.$fEqAssociativity updating EPS_ } ending fork Declaration for $fEqAssociativity } ending fork Dict fun GHC.Classes.$fEqAssociativity Starting fork { Declaration for Associativity Loading decl for GHC.Generics.Associativity updating EPS_ tcIfaceDecl4 GHC.Generics.Associativity } ending fork Declaration for Associativity Starting fork { Dict fun GHC.Classes.$fEqArity Starting fork { Declaration for $fEqArity Loading decl for GHC.Classes.$fEqArity updating EPS_ } ending fork Declaration for $fEqArity } ending fork Dict fun GHC.Classes.$fEqArity Starting fork { Declaration for Arity Loading decl for GHC.Generics.Arity updating EPS_ tcIfaceDecl4 GHC.Generics.Arity } ending fork Declaration for Arity Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} Reading interface for ghc-prim:GHC.Tuple; reason: Need home interface for wired-in thing (,,,,,,,,,,,,,,) readIFace /usr/local/google/src/ghc/libraries/ghc-prim/dist-install/build/GHC/Tuple.hi updating EPS_ } ending fork Declaration for $fEq(,,,,,,,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,,) Starting fork { Declaration for $fEq(,,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,,) Starting fork { Declaration for $fEq(,,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,,) Starting fork { Declaration for $fEq(,,,,,) Loading decl for GHC.Classes.$fEq(,,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,,) Starting fork { Declaration for $fEq(,,,,) Loading decl for GHC.Classes.$fEq(,,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,,) Starting fork { Declaration for $fEq(,,,) Loading decl for GHC.Classes.$fEq(,,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,,) } ending fork Dict fun GHC.Classes.$fEq(,,,) Starting fork { Dict fun GHC.Classes.$fEq(,,) Starting fork { Declaration for $fEq(,,) Loading decl for GHC.Classes.$fEq(,,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,,) } ending fork Dict fun GHC.Classes.$fEq(,,) Starting fork { Dict fun GHC.Classes.$fEq(,) Starting fork { Declaration for $fEq(,) Loading decl for GHC.Classes.$fEq(,) updating EPS_ Considering whether to load ghc-prim:GHC.Tuple {- SYSTEM -} } ending fork Declaration for $fEq(,) } ending fork Dict fun GHC.Classes.$fEq(,) Starting fork { Dict fun GHC.Classes.$fEq() Starting fork { Declaration for $fEq() Loading decl for GHC.Classes.$fEq() updating EPS_ Considering whether to load ghc-prim:GHC.Unit {- SYSTEM -} Reading interface for ghc-prim:GHC.Unit; reason: Need home interface for wired-in thing () readIFace /usr/local/google/src/ghc/libraries/ghc-prim/dist-install/build/GHC/Unit.hi updating EPS_ } ending fork Declaration for $fEq() } ending fork Dict fun GHC.Classes.$fEq() tcImportDecl GHC.Integer.Type.Integer Need decl for GHC.Integer.Type.Integer Considering whether to load integer-gmp:GHC.Integer.Type {- SYSTEM -} Reading interface for integer-gmp:GHC.Integer.Type; reason: Need decl for GHC.Integer.Type.Integer readIFace /usr/local/google/src/ghc/libraries/integer-gmp/dist-install/build/GHC/Integer/Type.hi updating EPS_ libraries/base/Data/Maybe.hs:70:13: Can't find interface-file declaration for type constructor or class integer-gmp:GHC.Integer.Type.Integer Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error When deriving the instance for (Eq (Maybe a))

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