March 2015 - ghc-tickets

[GHC] #9360: GHCi: Behave nicely on `-e`, like `ghc` and other programs
by GHC 19 Oct '15

19 Oct '15

#9360: GHCi: Behave nicely on `-e`, like `ghc` and other programs -------------------------------------+------------------------------------- Reporter: mcandre | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Like many programming language environments, GHC offers a handy `-e` option for evaluating an expression, then returning to the shell. {{{ $ ghc -e '2 + 2' 4 }}} One would expect the interpreter, GHCi, to offer a similar flag, but it surprisingly rejects it. {{{ ghci -e '2 + 2' ghc: on the commandline: cannot use `--interactive' with `-e' Usage: For basic information, try the `--help' option. }}} I think this behavior is quite unintuitive--when I pass `-e <exp>` to ghci, or pass `--interactive -e <exp>` to ghc, I expect the expression to be evaluated as the leading expression in an interactive interpreter session. Could we please tweak ghc like this to make it slightly more intuitive when these flags are used together? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9360> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10216: Allow arr ∧ (first ∨ (***)) as minimal definition of Arrow instance
by GHC 13 Oct '15

13 Oct '15

#10216: Allow arr ∧ (first ∨ (***)) as minimal definition of Arrow instance -------------------------------------+------------------------------------- Reporter: strake888 | Owner: ekmett Type: bug | Status: new Priority: normal | Milestone: Component: Core | Version: 7.10.1 Libraries | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10216> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9319: nofib-analyze doesn’t provide per-benchmark compile time/alloc numbers
by GHC 08 Oct '15

08 Oct '15

#9319: nofib-analyze doesn’t provide per-benchmark compile time/alloc numbers -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: NoFib benchmark | Version: 7.8.2 suite | Differential Revisions: Keywords: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------- The compile time and allocation numbers calculated by nofib are only available per module. While this is useful to find the cause of problems, it would be nice if these numbers were also accumulated for each benchmark, for easy of general analysis and uniformity, especially with automated monitoring of benchmark numbers. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9319> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10153: GHC mode for converting files to explicit layout
by GHC 08 Oct '15

08 Oct '15

#10153: GHC mode for converting files to explicit layout -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature | Status: new request | Milestone: Priority: low | Version: 7.11 Component: Compiler | Operating System: Unknown/Multiple (Parser) | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- One area where GHC is a little less friendly to newcomers is its Byzantine whitespace layout rules. Once you've gotten used to using GHC you can usually get what you want by abiding certain style, but before then it might be useful to see how GHC is inserting semicolons to your document. I don't think this would be too hard to do. The idea is to get the token stream and look for virtual curlies with no location. Once you have a list of them, you can go over the original buffer again and insert a brace or semicolon whenever you see a token like this. Might be a good beginner task. This function would also be useful for debugging layout, since knowing if semicolons are being inserted is useful. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10153> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9058: System.IO.openTempFile does not scale
by GHC 07 Oct '15

07 Oct '15

#9058: System.IO.openTempFile does not scale ------------------------------------+------------------------------------- Reporter: slyfox | 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: | ------------------------------------+------------------------------------- In search of a bug in darcs http://bugs.darcs.net/issue2364 i've notice very bad property of openTempFile: it's pattern is very predictable and has O(n^2) of already created temp files. Predictability allows very fun bugs survive in buggy programs, like: {{{ thread1: (fn, fh) <- openTempFile "." "hello" renameFile fn "something" -- some time after when (some_rare_buggy_condition) $ -- oops, reused temp name, but too late, other thread killed it writeFileFile fn thread2: (fn, fh) <- openTempFile "." "hello" workWithFn fn -- nobody should touch it, right? }}} It's _very_ hard to debug data corruption when all temp files are named "foo${pid}" and sometimes "foo${pid+1}". And more serious bug: the more threads you have trying to create similar temps performance drops significantly: Attached program shows the following numbers: {{{ $ time ./bench-temps same 2000 real 0m2.795s user 0m1.516s sys 0m1.190s $ time ./bench-temps diff 2000 real 0m0.161s user 0m0.043s sys 0m0.115s }}} It's O(N^2) growing open() storm. https://github.com/ghc/ghc/blob/master/libraries/base/System/IO.hs#L465 {{{ FileExists -> findTempName (x + 1) }}} This is the source of the problem. I'd suggest always using random name for it. For portability reasons I suggest adding at least insecure random '''rand()''' value from C library. That way we will succeed in opening temp file at the first attempt. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9058> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8364: equip GHC with an accurate internal model of floating point
by GHC 07 Oct '15

07 Oct '15

#8364: equip GHC with an accurate internal model of floating point ----------------------------------------------+---------------------------- Reporter: carter | Owner: Type: feature request | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more than a week) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: ----------------------------------------------+---------------------------- currently there really isn't a systematic / portable story for doing compile time reduction / evaluation for floating point numbers. there are some folks in the larger haskell community who are working on high precision soft float implementations / modelling. Once that work becomes available, might be worth exploring having something like that for doing controlled high precision evaluation of intermediate expressions in ghc proper. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8364> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8335: Create more specialized entries to GC
by GHC 06 Oct '15

06 Oct '15

#8335: Create more specialized entries to GC ------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: task | 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: | ------------------------------------+------------------------------------- Consider this Cmm code (taken from #8326): {{{ {offset cFd: // stack check if ((Sp + -16) < SpLim) goto cFr; else goto cFs; cFr: // not enough place on the stack, call GC R2 = R2; R1 = A.f_closure; call (stg_gc_fun)(R2, R1) args: 8, res: 0, upd: 8; cFs: // scrutinize (x ># 0#) _sEU::I64 = R2; _sEV::I64 = %MO_S_Gt_W64(R2, 0); if (_sEV::I64 != 1) goto cFg; else goto cFo; cFg: // False branch Hp = Hp + 16; if (Hp > HpLim) goto cFy; else goto cFx; cFy: // not enough heap, call GC HpAlloc = 16; I64[Sp - 16] = cFf; R1 = _sEV::I64; I64[Sp - 8] = _sEU::I64; Sp = Sp - 16; call stg_gc_unbx_r1(R1) returns to cFf, args: 8, res: 8, upd: 8; cFf: // re-do the False branch _sEU::I64 = I64[Sp + 8]; Sp = Sp + 16; _sEV::I64 = R1; goto cFg; cFx: // RHS of False branch I64[Hp - 8] = GHC.Types.I#_con_info; I64[Hp] = -_sEU::I64; R1 = Hp - 7; call (P64[Sp])(R1) args: 8, res: 0, upd: 8; cFo: // True branch Hp = Hp + 16; if (Hp > HpLim) goto cFv; else goto cFu; cFv: // not enough heap, call GC HpAlloc = 16; I64[Sp - 16] = cFn; R1 = _sEV::I64; I64[Sp - 8] = _sEU::I64; Sp = Sp - 16; call stg_gc_unbx_r1(R1) returns to cFn, args: 8, res: 8, upd: 8; cFn: // re-do the True branch _sEU::I64 = I64[Sp + 8]; Sp = Sp + 16; _sEV::I64 = R1; goto cFo; cFu: // RHS of True branch I64[Hp - 8] = GHC.Types.I#_con_info; I64[Hp] = _sEU::I64; R1 = Hp - 7; call (P64[Sp])(R1) args: 8, res: 0, upd: 8; } }}} We perform two different calls to garbage collection here. Calling GC after making initial stack check obviously can't use any stack, so we pass parameter to GC in regsiters: {{{ R2 = R2; R1 = A.f_closure; call (stg_gc_fun)(R2, R1) args: 8, res: 0, upd: 8; }}} But in the calls that are made later on inside the function we do put some parameters on the stack, thus increasing stack usage: {{{ cFv: // not enough heap, call GC HpAlloc = 16; I64[Sp - 16] = cFn; R1 = _sEV::I64; I64[Sp - 8] = _sEU::I64; Sp = Sp - 16; call stg_gc_unbx_r1(R1) returns to cFn, args: 8, res: 8, upd: 8; }}} If we had more specialized entries to GC that would allow us to pass parameters in registers (or in some fixed memory location associated with TCO?) then this function would not require any stack at all. Note that there is a separate issue here - `_sEV` variable is in fact dead and should be eliminated (see #8327). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8335> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8920: Alternative GADT syntax
by GHC 05 Oct '15

05 Oct '15

#8920: Alternative GADT syntax ----------------------------------------------+---------------------------- Reporter: guest | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler (Parser) | Version: Keywords: gadts | 7.8.1-rc2 Architecture: Unknown/Multiple | Operating System: Difficulty: Moderate (less than a day) | Unknown/Multiple Blocked By: | Type of failure: Other Related Tickets: | Test Case: | Blocking: ----------------------------------------------+---------------------------- An alternative syntax for GADTs Instead of {{{ data Term x where K :: Term (a -> b -> a) S :: Term ((a -> b -> c) -> (a -> b) -> a -> c) Const :: a -> Term a (:@) :: Term (a -> b) -> (Term a) -> Term b }}} You can write {{{ data Term x = K :: Term (a -> b -> a) | S :: Term ((a -> b -> c) -> (a -> b) -> a -> c) | Const a :: Term a | (:@) (Term (a -> b)) (Term a) :: Term b }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8920> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10071: Implement warnings for class-method overriding
by GHC 04 Oct '15

04 Oct '15

#10071: Implement warnings for class-method overriding -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: feature | Status: new request | Milestone: 7.12.1 Priority: normal | Version: 7.8.4 Component: Compiler | Operating System: Unknown/Multiple Keywords: AMP | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: #8004, #4384 Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- This would aid long-term transitions like phasing out `Monad(return)` (in the spirit of #4834): With the AMP, `Monad(return)` being a class method becomes an historic artifact. The ideal long-term situation would rather be to have `return` become a top-level definition (i.e. outside the `Monad`-class), generalised to `Applicative` just aliasing `Applicative(pure)`, i.e. {{{#!hs return :: Applicative f => a -> f a return = pure }}} This may be beneficial for things like ApplicativeDo which otherwise would require a `return` to be handled is if it was `pure` in order to weaken the type-constraint in an `do`-expression like e.g. {{{#!hs do { x <- f; return (fst x) } }}} Right now, we can attach a `DEPRECATE`-pragma to the `return`-class- method. That however would trigger warnings on ''all'' uses of `return`, rather than only when using `return` in a context that requires it to be a class-method (like overriding `return` in instance definitions, or importing/exporting it via the explicit `Monad(return)`-syntax) Instead we need a way to warn about such uses of `return` which assume it to be a class-method, in order to phase out such uses. NB: This will probably require additional discussions, but we shouldn't wait too long, if we want to integrate the AMP into a future Haskell Report (for which we should try to clean up historic warts such as `Monad(return)` if feasable). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10071> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9907: "Unknown PEi386 section name `.text$printf'" error in GHCi on Windows
by GHC 03 Oct '15

03 Oct '15

#9907: "Unknown PEi386 section name `.text$printf'" error in GHCi on Windows ----------------------------------+------------------------------------- Reporter: mmikolajczyk | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.8.3 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: GHCi crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: ----------------------------------+------------------------------------- I work on a Haskell library interfacing with foreign C++ library. While trying to use it in GHCi on Windows 8.1 64bit, I encountered an error message that said: {{{ <loading other libraries> Loading package library-0.1.0.0 ... <interactive>: Unknown PEi386 section name ` .text$_ZNSt6vectorIcSaIcEED1Ev' (while processing: c:\path\to\file.o) ghc.exe: panic! (the 'impossible' happened) (GHC version 7.8.3 for i386-unknown-mingw32): loadObj "C:\\path\\to\\file.o": failed Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I've prepared a minimal example triggering this bug and attached it to this bug report. On Linux (Arch 64bit), after cabal build and cabal repl it behaves as intended: {{{ GHCi, version 7.8.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading object (static) dist/build/cbits/ex.o ... done final link ... done [1 of 1] Compiling Example ( Example.hs, interpreted ) Ok, modules loaded: Example. λ: foo Test }}} However, on Windows 8.1 it crashes while loading object file: {{{ GHCi, version 7.8.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading object (static) dist\build\cbits\ex.o ... ghc.exe: Unknown PEi386 sectio n name `.text$printf' (while processing: dist\build\cbits\ex.o) ghc.exe: panic! (the 'impossible' happened) (GHC version 7.8.3 for i386-unknown-mingw32): loadObj "dist\\build\\cbits\\ex.o": failed Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Crashing in GHCi means that I cannot use it with programs that contain TH splices, what is important for me. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9907> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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