March 2016 - ghc-tickets

[GHC] #10262: Improve documentation of module signatures
by GHC 11 Jan '17

11 Jan '17

#10262: Improve documentation of module signatures -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.11 Documentation | Operating System: Unknown/Multiple Keywords: backpack | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Out of curiosity, I read the bit in the user manual about the new module signatures, and I find the text a little confusing. Could those in the know clarify the points below in the manual? Thanks! * (typo) The first example refers to `String.hs`. I think you mean `Text.hs`. * Is there a way to use module signatures to deal with mutually recursive modules? The example with `TextSig` seems to require that both `Text` and `TextSig` are compiled before `A`. * Could you provide an example of specifying multiple signature/implementation pairs with `--make`? * The manual says that the dialect of Haskell used in signature files is "essentially" the same as with hs-boot files. Are there any differences? * The most recent paragraph addition doesn't make sense to me, starting with "Signatures can be installed like ordinary modules". What do you mean by "installed"? What does it mean to bring multiple signatures into scope by the same name? Can two signatures have the same name? Wouldn't their filenames also need to be the same? * Is there currently any facility available to have multiple implementations of one signature? Of course, this is all work in progress, and I don't necessarily expect an immediate fix. But, when it's nearing completion, it may be worth revisiting this stretch of text. Thanks! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10262> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11592: Self-kinded type varialbe accepted
by GHC 10 Jan '17

10 Jan '17

#11592: Self-kinded type varialbe accepted -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- Found when chasing #11407 {{{ data T (a::a) = Blah -- Accepted data S (b :: a) a = ... -- Rejected with: variable ‘a’ used as a kind variable before being bound -- as a type variable. Perhaps reorder your variables? }}} But `T` should be rejected too, for the same reason as `S` -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11592> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11040: Split SRT tables on Mac OS
by GHC 10 Jan '17

10 Jan '17

#11040: Split SRT tables on Mac OS ----------------------------------------+--------------------------------- Reporter: olsner | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- Split off from https://phabricator.haskell.org/D1242#inline-11490 Mac uses subsections via symbols to allow dead code stripping, but doesn't seem to do anything special with the SRT tables (in `HscMain.doCodeGen`), so either I'm missing something or Mac doesn't actually get much useful dead code stripping at all from the subsections feature because the SRT tables would keep everything alive. Perhaps Mac should just always do SRT splitting. Looks like you need to manually add `-optl-Wl,-dead_strip` to test this, since that's not enabled by default. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11040> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11551: Get doctests into testsuite
by GHC 10 Jan '17

10 Jan '17

#11551: Get doctests into testsuite -------------------------------------+------------------------------------- Reporter: lwm | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Core | Version: 7.10.3 Libraries | Keywords: | Operating System: Unknown/Multiple documentation, doctest | Architecture: | Type of failure: Documentation Unknown/Multiple | bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It seems like a bit of a shame not to have Mr.Orlitzky's lovely doctests not running with the testsuite. Or perhaps to at least have some sort of `make doctest`. If there is some interest to get this working, I'd like to take a look at submitting a patch. Here are the previous documentation patches I can find: https://phabricator.haskell.org/p/mjo/ I can see the following files that have doctests: {{{ ruby-2.2.1 ~/work/contributing/ghc (master) [12:35:44] lwm$ grep -R "=== __Examples__" libraries/base/ | uniq grep: libraries/base/Data/Maybe.hs:-- ==== __Examples__ libraries/base/Data/Either.hs:-- ==== __Examples__ libraries/base/Data/List.hs:-- ==== __Examples__ libraries/base/Data/Functor.hs:-- ==== __Examples__ libraries/base/Data/Bool.hs:-- ==== __Examples__ libraries/base/Data/Char.hs:-- ==== __Examples__ libraries/base/GHC/Unicode.hs:-- ==== __Examples__ libraries/base/Text/Printf.hs:-- ==== __Examples__ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11551> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8761: Make pattern synonyms work with Template Haskell
by GHC 10 Jan '17

10 Jan '17

#8761: Make pattern synonyms work with Template Haskell ------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | 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: | ------------------------------------+------------------------------------- Template Haskell has no support for pattern synonyms. This should be added. Specifically: * Create syntax in `Language.Haskell.TH.Syntax` and corresponding functions in `Language.Haskell.TH.Lib` * Support in !DsMeta for desugaring pattern synonym quotations. See `rep_bind`. * Support in Convert for splicing in pattern synonyms. * Support in !TcSplice for reifying pattern synonyms. See `reifyThing`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8761> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9748: Disambiguate IO actions in GHCi with :set +t
by GHC 06 Jan '17

06 Jan '17

#9748: Disambiguate IO actions in GHCi with :set +t -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: GHCi | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 | Type of failure: hour) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Currently GHCi's `:set +t` displays the same type for the following: {{{#!hs % ghci -ignore-dot-ghci GHCi, version 7.8.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :set +t Prelude> 'a' 'a' it :: Char Prelude> return 'a' 'a' it :: Char Prelude> return 'a' :: IO Char 'a' it :: Char }}} A user at `#haskell-beginners` ran into a problem where they mistook an expression that defaulted to IO for a pure expression (`Id . even <$> pure 5`), `:set +t` was suggested but ended up showing the incorrect type: {{{#!hs ghci> Id . even <$> pure 5 Id False it :: Id Bool }}} This is bad for pedagogical reasons, it would be an improvement to display the following: {{{#!hs Prelude> :set +t Prelude> 'a' 'a' it :: Char Prelude> return 'a' 'a' it :: Char <- return 'a' :: IO Char Prelude> return 'a' :: IO Char 'a' it :: Char <- return 'a' :: IO Char }}} mirroring existing syntax: {{{#!hs Prelude> :set -XScopedTypeVariables Prelude> a :: Char <- return 'a' :: IO Char a :: Char }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9748> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10352: Properly link Haskell shared libs on ELF systems
by GHC 05 Jan '17

05 Jan '17

#10352: Properly link Haskell shared libs on ELF systems -------------------------------------+------------------------------------- Reporter: duncan | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Package | Version: 7.11 system | Operating System: Linux Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Since the early days of building Haskell shared libs on Linux we have been using a scheme that is really a bit of a hack. We should do it properly. In my blog post on this from 2009 (http://www.well-typed.com/blog/30/) I said: > If we use ldd again to look at the libfoo.so that we've made we will notice that it is missing a dependency on the rts library. This is problem that we've yet to sort out, so for the moment we can just add the dependency ourselves: > > $ ghc --make -dynamic -shared -fPIC Foo.hs -o libfoo.so \ > -lHSrts-ghc6.11 -optl-Wl,-rpath,/opt/ghc/lib/ghc-6.11/ > > The reason it's not linked in yet is because we need to be able to switch which version of the rts we're using without having to relink every library. For example we want to be able to switch between the debug, threaded and normal rts versions. It's quite possible to do this and it just needs a bit more rearranging in the build system to sort it out. Once it's done you'll even be able to switch rts at runtime, eg: > > $ LD_PRELOAD=/opt/ghc/lib/ghc-6.11/libHSrts_debug-ghc6.11.so > $ ./Hello So in general, if a shared lib requires symbols from another shared lib then it should depend on it. In ELF terminology that means a NEEDED entry to say this lib needs that other lib. This is important to be able to link and load these shared libraries, otherwise they can have dangling dependencies. But we don't do this. For the specific case of the RTS we do not link Haskell shared libs against the RTS. So they have lots of dangling symbols. These libraries cannot be loaded on their own, e.g. with `dlopen()`. This is bad, and has other knock-on consequences. Why don't we link to the RTS? It's because historically (with static linking) GHC had had the ability to select the flavour of the RTS when final executables are linked, not when intermediate libraries are created. This works because the RTS flavours share a common ABI. This is a useful feature as it lets us select the SMP or debug or other RTS at final link time. So when we made up the first shared lib scheme on ELF we had to support this. Our initial scheme was like this: don't link Haskell library DSOs against the RTS, only like the final exe against the RTS. Each RTS flavour has a separate SONAME, e.g. `libHSrts_thr-ghc7.8.4.so` or `libHSrts_debug- ghc7.8.4.so`. This works because the runtime linker looks at the final exe first and loads the RTS, and then when other libs are loaded the symbols all resolve. Why can't we link all the libraries against the RTS? Currently each RTS flavour has a different SONAME, which is the key that the dynamic linker uses to identify each library. So if we did link all the Haskell libs against "the" RTS we would have to pick which one at the point at which we create the library, and that'd stop us from being able to choose later. So, can we use a better scheme? We want one that doesn't leave dangling undefined references in intermediate Haskell libs, and is also compatible with the ability to select the flavour of the RTS at final exe link time (or even override it at load time). Yes we can! The first thing to note is that to be interchangeable, all the RTS flavours (that share a compatible ABI) need to have the same SONAME. So for example, all the (non-profiling) RTS DSO files have to have the internal SONAME of `libHSrts-ghc7.8.4.so`. Once they all have the same SONAME, then it's ok for all the Haskell libs to specify a NEEDED dependency on that rts SONAME. But if they have the same SONAME, what do the files get called, where do they live and how are they found? The trick is to make use of the search path. Put each RTS flavour in a different directory, but otherwise with the same filename, e.g. `lib/rts-1.0/thr/libHSrts-ghc7.8.4.so`, `lib/rts-1.0/debug/libHSrts-ghc7.8.4.so` etc. Each library DSO and exe has its list of NEEDED entries, and it has an RPATH entry used to find those libraries if they're not loaded yet. The key is the "if they're not loaded yet" bit. Remember that the linker uses the SONAME as the key to decide if the lib is loaded yet or not. So the libraries could all have an RPATH entry to say to look for the RTS in the directory containing the default RTS flavour. But then the top level exe (or foreign/export shared lib) can also link to the RTS directly (ie an NEEDED entry) and can specify an RPATH which can be for any of the rts flavours. When the linker loads the top level exe, it will loads the selected RTS using the exe's RPATH, and then when the linker sees other Haskell libs that have a NEEDED entry on the RTS it will ignore them because the RTS's SONAME is already loaded. So concretely, instead of: lib/ghc-${ver}/rts-1.0/libHSrts-ghc${ver}.so lib/ghc-${ver}/rts-1.0/libHSrts_thr-ghc${ver}.so lib/ghc-${ver}/rts-1.0/libHSrts_debug-ghc${ver}.so lib/ghc-${ver}/rts-1.0/libHSrts_l-ghc${ver}.so lib/ghc-${ver}/rts-1.0/libHSrts_thr_l-ghc${ver}.so lib/ghc-${ver}/rts-1.0/libHSrts_thr_debug-ghc${ver}.so each with a different SONAME we'd have lib/ghc-${ver}/rts-1.0/libHSrts-ghc${ver}.so lib/ghc-${ver}/rts-1.0/thr/libHSrts-ghc${ver}.so lib/ghc-${ver}/rts-1.0/debug/libHSrts-ghc${ver}.so lib/ghc-${ver}/rts-1.0/l/libHSrts-ghc${ver}.so lib/ghc-${ver}/rts-1.0/thr_l/libHSrts-ghc${ver}.so lib/ghc-${ver}/rts-1.0/thr_debug/libHSrts-ghc${ver}.so each with the same SONAME When linking libs we would always use `-lHSrts -rpath lib/ghc-${ver}/rts-1.0` When linking exes (or shared libs for external consumption) we would use both `-lHSrts` and `-rpath lib/ghc-${ver}/${rtsflavour}/rts-1.0`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10352> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9248: Document -XHaskell98 and -XHaskell2010 in flag reference
by GHC 05 Jan '17

05 Jan '17

#9248: Document -XHaskell98 and -XHaskell2010 in flag reference ------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Documentation | 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: | ------------------------------------+------------------------------------- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9248> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11096: Builtin encoder/decoder should be used for Latin-1
by GHC 05 Jan '17

05 Jan '17

#11096: Builtin encoder/decoder should be used for Latin-1 -------------------------------------+------------------------------------- Reporter: bgamari | Owner: hvr Type: feature | Status: new request | Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.2 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: -------------------------------------+------------------------------------- Filed on behalf of hvr. Currently `mkTextEncoding'` delegates decoding/encoding from/to latin-1 to `iconv`. This shouldn't be necessary as we have latin-1 an encoder in `base`. Let's use it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11096> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10680: Make Backpack order-independent (again)
by GHC 04 Jan '17

04 Jan '17

#10680: Make Backpack order-independent (again) -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: normal | Milestone: Component: Package | Version: 7.11 system | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- When we moved to the new `bkp` file format, we also went back to the a format which is order-dependent: that is to say, the order in which you put the declarations matters. So if you write: {{{ unit p where module A where import B module B where ... }}} this fails to type-check, GHC complaining that `B` is not in scope. I did this, in part because it's what the Backpack paper described, and because it was "simpler" to implement. I think we should move back to an order-independent scheme, for the following reasons: 1. Haskell users are used to not needing pay particularly close attention to the ordering of their modules, and forcing people to linearize their module descriptions would be spectacularly disruptive with large amounts of modules. So un-ordered modules are "more natural. 2. Order-independence imposes some constraints on how expressive programs are (with order-dependent Backpack, you can do some pretty tricky things by ordering things certain ways); this could simplify some aspects of compiler implementation and make Backpack easier to explain. 3. A particular case of (2): it seems a lot simpler UX-wise to let a user assume that if you import a module `M` in a unit, it doesn't matter where you import it: you always get the same set of identifiers brought into scope. Thus, the incremental results of signatures should not be visible, c.f. #10679 The main idea is that only the surface-syntax is un-ordered: the internal representation of units is a DAG which we work out in an elaboration phase, not altogether unsimilar from what `GhcMake` computes. Here are the details: **The intermediate representation.** We translate into an intermediate representation which consists of a directed graph between modules, signatures and includes. Edges in the graph indicate a "depends on" relation: 1. `include p` depends on `include q` if, for some module name `H`, `p` requires `H` and `q` provides `H`. 2. A module/signature `M` depends on `include p` if `M` imports a module provided or required by `p`. 3. A module/signature `M` depends on a module/signature `S` if `M` imports `S`. 4. An `include p` depends on a module `M` if `p` requires a module named `M`. (This rule is included for completeness; we are going to disallow it shortly.) We impose one restriction: a signature cannot depend on a home module. See below for how to eliminate this restriction. Rule (2) is worth remarking upon: if a module imports a signature, it depends-on every `include` which requires that signature, as well as the relevant home signature. This could easily result in a cycle; see (2) for how to break these cycles. The consequence of this, however, is that we can factor the graph to introduce the node for the "merge of signatures", which depends on each signature and include which requires it; we can use this opportunity to build and write out the merged interface file for the unit. **Elaboration.** Take a Backpack file, construct this graph, and topsort it into a DAG of SCCs. SCCs with a single node are compileable as before. SCCs with multiple nodes will have to be managed with some mutual recursion mechanism; see refinements for more thoughts on this. **Refinements:** 1. **Can a signature depend on a (home) module?** Imports of this kind require a retypecheck loop. Consider this situation: {{{ unit p where signature H where data T module M where import H data S = S T unit q where include p module Q where import M signature H where import Q data T = T S }}} Here, signature H in q depends on Q. When we typecheck `Q`, we bring `M.S` into the type environment with a `TyThing` that describes the constructor as accepting an abstract type `T`. However, when we subsequently typecheck the local signature `H`, we must refine all `TyThing`s of `T` with the true description (e.g. constructor information). So you'll need to retypecheck `Q` (and `M`) in order to make sure the `TyThing` is correct. 2. **Can an include depend on a (home) module?** If the module has no (transitive) dependency on signatures, this is fine. However, it's easy to have a circular dependency. Consider: {{{ unit p where signature A signature B module M unit q where include p module B where import A ... }}} `B` depends on `p` for `p/A.hsig`; however, `p` depends on `B` because this module is filling a requirement. Fortunately, we can untangle this knot without any mutual recursion nonsense (and the attendant efficiency loss): `A` is just an export list, we can compute it from the abstractly type-checked version of `p` without instantiating `B`. 3. **Can we deal with include-include dependency cycles?** Yes! Just use the Backpack paper's strategy for creating a recursive unit key and compile the two packages `hs-boot` style. But I'm not planning on implementing this yet. 4. **Can we deal with signature-signature dependency cycles?** Ordered Backpack would have supported this: {{{ unit a-sig where signature A where data T unit ab-sig where include a-sig signature B where import A data S = S T signature A where import B data T = T S }}} In our model, `ab-sig` has a cycle. However, I believe any such cycle can be broken by creating sufficiently many units: {{{ unit a-sig where signature B where data T signature A where data S = S T unit b-sig where signature A where data S signature B where data T = T S unit ab-sig where include a-sig include b-sig }}} In principle, GHC could automatically break import cycles by replacing an import with an import of a reduced signature that simply has abstract type definitions. (I'm not sure this is possible for all language features.) This technique would also work for normal modules, assuming that every function is explicitly annotated with a type. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10680> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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