February 2016 - ghc-tickets

[GHC] #9334: Implement "instance chains"
by GHC 09 Aug '18

09 Aug '18

#9334: Implement "instance chains" -------------------------------------+------------------------------------- Reporter: diatchki | Owner: diatchki Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.9 checker) | Differential Revisions: Keywords: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------- It would be useful to implement a version of "instance chains" [1] in GHC, which would eliminate the need for OVERLAPPING_INSTANCES in most (all practcial?) programs. The idea is that programmers can explicitly group and order instances into an "instance chain". For example: {{{ instance (Monad m) => StateM (StateT s m) s where ... else (MonadTrans t, StateM m s) => StateM (t m) s where ... }}} When GHC searches for instances, the instances in a chain are considered together and in order, starting with the first one: 1. If the goal matches the current instance's head, then this instance is selected and the rest are ignored, as if they were not there; 2. If the goal does not match the current instance's head, AND it does not unify with the current instance's head, then we skip the instance and proceed to the next member of the chain; 3. If the goal does not match the current instance's head, but it does unify with it, then we cannot use this chain to solve the goal. In summary: earlier instances in a chain "hide" later instances, and later instances can be reached only if we are sure that none of the previous instance will match. [1] http://web.cecs.pdx.edu/~mpj/pubs/instancechains.pdf -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9334> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10927: IndexError: pop from empty list
by GHC 08 Aug '18

08 Aug '18

#10927: IndexError: pop from empty list -------------------------------------+------------------------------------- Reporter: schwab | Owner: hvr Type: bug | Status: new Priority: normal | Milestone: Component: Trac & Git | Version: Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | -------------------------------------+------------------------------------- ==== Zum Reproduzieren ==== Während der Ausführung von GET auf `/attachment/ticket/10926/` hat Trac einen internen Fehler gemeldet. ''(Bitte geben Sie hier weitere Details an)'' Anfrageparameter: {{{ {u'action': u'new', 'path': u'10926/', 'realm': u'ticket'} }}} User agent: `Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.21 (KHTML, like Gecko) konqueror/4.14.9 Safari/537.21` ==== Systeminformationen ==== ''Systeminformation nicht verfügbar'' ==== Aktive Plugins ==== ''Plugininformation nicht verfügbar'' ==== Python-Zurückverfolgungsinformationen ==== {{{ Traceback (most recent call last): File "/usr/local/lib/python2.7/dist- packages/Trac-1.0.9-py2.7.egg/trac/web/main.py", line 554, in _dispatch_request dispatcher.dispatch(req) File "/usr/local/lib/python2.7/dist- packages/Trac-1.0.9-py2.7.egg/trac/web/main.py", line 267, in dispatch iterable=chrome.use_chunked_encoding) File "/usr/local/lib/python2.7/dist- packages/Trac-1.0.9-py2.7.egg/trac/web/chrome.py", line 1111, in render_template encoding='utf-8') File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 184, in render return encode(generator, method=method, encoding=encoding, out=out) File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 58, in encode for chunk in iterator: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 350, in __call__ for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 829, in __call__ for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 669, in __call__ for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 774, in __call__ for kind, data, pos in chain(stream, [(None, None, None)]): File "/usr/local/lib/python2.7/dist-packages/genshi/output.py", line 594, in __call__ for ev in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist- packages/Trac-1.0.9-py2.7.egg/trac/web/chrome.py", line 1309, in _strip_accesskeys for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist- packages/Trac-1.0.9-py2.7.egg/trac/web/chrome.py", line 1298, in _generate for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 706, in _unmark for mark, event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 1101, in __call__ for mark, event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 118, in __iter__ event = self.stream.next() File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 734, in __call__ for mark, event in stream: File "/usr/local/lib/python2.7/dist- packages/genshi/filters/transform.py", line 702, in _mark for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 378, in _match ctxt, start=idx + 1, **vars): File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 378, in _match ctxt, start=idx + 1, **vars): File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 362, in _match content = list(content) File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 326, in _match for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 315, in _strip event = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 558, in _flatten for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/path.py", line 588, in _generate subevent = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 315, in _strip event = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 558, in _flatten for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/core.py", line 289, in _ensure for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/path.py", line 588, in _generate subevent = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 618, in _include for event in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/template/markup.py", line 315, in _strip event = next() File "/usr/local/lib/python2.7/dist-packages/genshi/template/base.py", line 558, in _flatten for kind, data, pos in stream: File "/usr/local/lib/python2.7/dist-packages/genshi/filters/i18n.py", line 178, in _generate for event in msgbuf.translate(gettext(msgbuf.format())): File "/usr/local/lib/python2.7/dist-packages/genshi/filters/i18n.py", line 1051, in translate events = self.events[order].pop(0) IndexError: pop from empty list }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10927> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10599: Template Haskell doesn't allow `newName "type"`
by GHC 07 Aug '18

07 Aug '18

#10599: Template Haskell doesn't allow `newName "type"` -------------------------------------+------------------------------------- Reporter: meteficha | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 7.10.1 Haskell | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Using `type` as a name is, of course, forbidden. OTOH, `type_1` is allowed as a name. However, using GHC 7.10.1 and `ghc --make T.hs` on files: {{{#!hs -- T.hs {-# LANGUAGE TemplateHaskell #-} module T where import Q test -- Q.hs module Q where import Language.Haskell.TH test :: Q [Dec] test = do t <- newName "type" return [FunD t [Clause [] (NormalB $ LitE $ CharL 't') []]] }}} Leads to the following error: {{{ $ ghc --make -ddump-splices T.hs [2 of 2] Compiling T ( T.hs, T.o ) T.hs:6:1: Illegal variable name: ‘type’ When splicing a TH declaration: ident_0 type_1 = type_1 }}} The above example works fine for GHC 7.8.4, so it's a regression. Reference: https://github.com/yesodweb/persistent/issues/412 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10599> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10355: Dynamic linker not initialised
by GHC 07 Aug '18

07 Aug '18

#10355: Dynamic linker not initialised -------------------------------------+------------------------------------- Reporter: dpiponi | 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: | -------------------------------------+------------------------------------- I get this message: [ 3 of 24] Compiling Cable ( src/Cable.hs, dist/build/ui/ui- tmp/Cable.o ) <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.10.1 for x86_64-apple-darwin): Dynamic linker not initialised Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug when building my code here: https://github.com/dpiponi/Moodler/tree/master/Moodler/src under Yosemite 10.10.2 So I'm reporting it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10355> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9868: ghc: panic! Dynamic linker not initialised
by GHC 07 Aug '18

07 Aug '18

#9868: ghc: panic! Dynamic linker not initialised -------------------------------------+------------------------------------- Reporter: Jamedjo | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: MacOS X Architecture: x86_64 (amd64) | Type of failure: Compile- Difficulty: Unknown | time crash Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I was playing around and not expecting cabal build to succeed yet. If if didn't say the impossible had happened I would assumed I was missing something and used the error to drive my next action {{{ <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-apple-darwin): Dynamic linker not initialised Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} There had been another error before: {{{ <no location info>: <command line>: can't load .so/.DLL for: /Users/JamesEJ/bindings- cef3/dist/build/libHSbindings-cef3-0.1.0-ghc7.8.3.dylib (dlopen(/Users/JamesEJ/bindings-cef3/dist/build/libHSbindings- cef3-0.1.0-ghc7.8.3.dylib, 9): Symbol not found: _cef_add_cross_origin_whitelist_entry Referenced from: /Users/JamesEJ/bindings-cef3/dist/build/libHSbindings- cef3-0.1.0-ghc7.8.3.dylib Expected in: flat namespace in /Users/JamesEJ/bindings-cef3/dist/build/libHSbindings- cef3-0.1.0-ghc7.8.3.dylib) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9868> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10087: DefaultSignatures: error message mentions internal name
by GHC 02 Aug '18

02 Aug '18

#10087: DefaultSignatures: error message mentions internal name -------------------------------------+------------------------------------- Reporter: | Owner: andreas.abel | Status: new Type: feature | Milestone: request | Version: 7.8.4 Priority: normal | Operating System: Unknown/Multiple Component: Compiler | Type of failure: Other (Type checker) | Blocked By: Keywords: | Related Tickets: Architecture: | Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE DefaultSignatures #-} class C a where reflexive :: a -> Bool default reflexive :: Eq a => a -> Bool reflexive x = x == x data D instance C D where -- /home/abel/play/haskell/bugs/DefaultSig.hs:10:10: -- No instance for (Eq D) arising from a use of ‘Main.$gdmreflexive’ -- In the expression: Main.$gdmreflexive -- In an equation for ‘reflexive’: reflexive = Main.$gdmreflexive -- In the instance declaration for ‘C D’ }}} Error looks odd: The user has not written $gdmreflexive in his code. TODO: Better error message. Maybe this should just trigger a warning that method {{{reflexive}}} is undefined for instance {{{D}}} of {{{C}}}. Like when I remove the default method. {{{ /home/abel/play/haskell/bugs/DefaultSig.hs:10:10: Warning: No explicit implementation for ‘reflexive’ In the instance declaration for ‘C D’ }}} It seems the semantics of a default signature is that each instance *must* implement this method. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10087> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10056: Inconsistent precedence of ~
by GHC 30 Jul '18

30 Jul '18

#10056: Inconsistent precedence of ~ -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 (Parser) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: | valid program Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following compiles as expected: {{{#!hs {-# LANGUAGE TypeFamilies #-} type family Foo a b f :: (Foo a b ~ Int) => a -> b -> b f = error "" }}} but this fails: {{{#!hs {-# LANGUAGE TypeFamilies #-} type family a \\ b f :: (a \\ b ~ Int) => a -> b -> b f = error "" }}} with the error > "The second argument of `(\\)` should have kind `*`, but `b ~ Int` has kind `Constraint`." Thus the first example is being parsed as `(Foo a b) ~ Int`, while the second is parsed as `a \\ (b ~ Int)`. I believe the second example should compile, i.e. `(\\)` and `Foo` should have the same precedence, both of which are higher than `(~)`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10056> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11549: Add -fshow-runtime-rep
by GHC 29 Jul '18

29 Jul '18

#11549: Add -fshow-runtime-rep -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As discussed in several interwoven threads ([https://mail.haskell.org/pipermail/ghc-devs/2016-February/011268.html original], [https://mail.haskell.org/pipermail/haskell- cafe/2016-February/122914.html café]), it has been suggested to add a flag `-fshow-runtime-rep`. Without this flag enabled, the pretty printer will instantiate any `RuntimeRep` type parameters to `PtrRep Lifted`. This has the effect of changing {{{ ($) :: forall (r :: RuntimeRep) (a :: *) (b :: TYPE r). (a -> b) -> a -> b }}} to {{{ ($) :: (a -> b) -> a -> b }}} under the default GHCi settings. Note that `Levity` becomes `RuntimeRep` after #11471 is complete. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11549> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10184: Coercible solver incomplete with recursive newtypes
by GHC 29 Jul '18

29 Jul '18

#10184: Coercible solver incomplete with recursive newtypes -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: low | Milestone: ⊥ Component: Compiler | Version: 7.10.1-rc3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following module fails to compile due to infinite recursion: {{{ import Data.Coerce newtype Bar a = Bar (Either a (Bar a)) newtype Age = MkAge Int x :: Bar Age x = coerce (Bar (Left (5 :: Int))) }}} It tries to coerce `Bar Int` to `Bar Age`. This is clearly doable, via tyconapp decomposition. But we don't find it. Before worrying too much about it, though, we'll wait for a real example. Do speak up if this problem is ruining your day! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10184> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9936: Data.Fixed truncates 5.17 to 5.16
by GHC 28 Jul '18

28 Jul '18

#9936: Data.Fixed truncates 5.17 to 5.16 -------------------------------------+------------------------------------- Reporter: singpolyma | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.6.3 libraries/base | Operating System: Unknown/Multiple Keywords: | Type of failure: Incorrect result Architecture: | at runtime Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- `(realToFrac (5.17 :: Double) :: Centi) == 5.16` is true -- it should be false. The offender seems to be the assumption in `fromRational`: `fromRational r = withResolution (\res -> MkFixed (floor (r * (toRational res))))` Uses `floor` assuming that the underlying floating point value is stored purely and not as 0.999999 or similar -- switching it to `round` fixes this issue. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9936> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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