October 2015 - ghc-tickets

[GHC] #9149: Description of openFileBlocking is wrong
by GHC 25 Jan '16

25 Jan '16

#9149: Description of openFileBlocking is wrong ------------------------------------+------------------------------------- Reporter: edsko | Owner: 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: | ------------------------------------+------------------------------------- The documentation states: ''Like openFile, but opens the file in ordinary blocking mode. This can be useful for opening a FIFO for reading: if we open in non-blocking mode then the open will fail if there are no writers, whereas a blocking open will block until a writer appears. '' but I think this is the wrong way around, and should be: ''Like openFile, but opens the file in ordinary blocking mode. This can be useful for opening a FIFO for writing: if we open in non-blocking mode then the open will fail if there are no readers, whereas a blocking open will block until a reader appears. '' -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9149> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10751: Implement Phase 1 of MonadFail Proposal (MFP)
by GHC 25 Jan '16

25 Jan '16

#10751: Implement Phase 1 of MonadFail Proposal (MFP) -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: task | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.10.2 Keywords: report- | Operating System: Unknown/Multiple impact | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- See also - https://www.reddit.com/r/haskell/comments/3a1o06/monadfail_proposal_mfp/ TODO: At this point this ticket is mostly a reminder that stuff may need to be done for GHC 7.12 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10751> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10560: -f and -O options interact in non-obvious, order dependent ways
by GHC 25 Jan '16

25 Jan '16

#10560: -f and -O options interact in non-obvious, order dependent ways -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- The `-O[012]` and `-f*` flags are both implemented by manipulating a set of flags in `DynFlags`. These manipulations occur in the order that the flags occur in the command line. This leads to some rather surprising behavior. For instance, if the user wants to compile with optimization but specifically wants to disable specialisation, they might enter `-fno- specialise -O1`. This, however, would not do what the user expects as `-O1` implies `-fspecialise`, overriding the first flag. This is surprising and poorly documented behavior at best. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10560> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8325: Pattern guards in anonymous functions
by GHC 25 Jan '16

25 Jan '16

#8325: Pattern guards in anonymous functions ------------------------------------+------------------------------------- Reporter: mcollis | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | 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: | ------------------------------------+------------------------------------- In the course of a project, I had an idea that would allow less cumbersome use of cases in anonymous functions. Here's a simple example of what I'm proposing: {{{ (\x y | x > y -> x | otherwise -> something else) }}} Currently, the only way to accomplish this is with if() then ... else syntax or the use of the MultiWayIf and LambdaCase extensions. The syntax I've proposed here matches with existing anonymous function syntax and doesn't conflict with any other GHC syntax. This would greatly improve the readability of complex anonymous functions. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8325> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9708: Type inference non-determinism due to improvement
by GHC 24 Jan '16

24 Jan '16

#9708: Type inference non-determinism due to improvement -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Here's an example that showed up in Iavor's test `TcTypeNatSimple`: {{{ ti7 :: (x <= y, y <= x) => Proxy (SomeFun x) -> Proxy y -> () ti7 _ _ = () }}} From the ambiguity check for `ti7` we get this constraint {{{ forall x y. (x <= y, y <= x) => ( SomeFun x ~ SomeFun alpha , alpha <= y, y <= alpha) }}} where `alpha` is the unification variable that instantiates `x`. Now, from the givens, improvement gives a derived `[D] x~y`, but we can't actually use that to rewrite anything; we have no evidence. From the wanteds we can use improvement in two alternative ways: {{{ 1. (alpha <= y, y <= alpha) => [D] alpha ~ y 2. (x <= y, y <= alpha) => [D] x <= alpha (alpha <= y, y <= x) => [D] alpha <= x And combining the latter two we get [D] (alpha ~ x) }}} It is (2) that we want. But if we get (1) and fix `alpha := y`, we get an error `Can't unify (SomeFun x ~ SomeFun y)`. I think it's a fluke that this test has been working so far; in my new flatten-skolem work it has started failing, which is not unreasonable. What I HATE is that whether type checking succeeds or fails depends on some random choice about which constraint is processed first. The real bug is that the derived Given has no evidence, and can't be used for rewriting. I think Iavor is fixing this deficiency for. I speculate that the same problem might also show up with ordinary type-class functional dependencies, but I have not found a concrete example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9708> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10223: Cleanup `mk/build.mk.sample`
by GHC 24 Jan '16

24 Jan '16

#10223: Cleanup `mk/build.mk.sample` -------------------------------------+------------------------------------- Reporter: thomie | Owner: thomie Type: task | Status: new Priority: normal | Milestone: 7.12.1 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: | -------------------------------------+------------------------------------- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10223> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8572: Building an empty module with profiling requires profiling libraries for integer-gmp
by GHC 24 Jan '16

24 Jan '16

#8572: Building an empty module with profiling requires profiling libraries for integer-gmp -------------------------------------------+------------------------------- Reporter: parcs | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.7 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- {{{ #!haskell {-# LANGUAGE NoImplicitPrelude #-} module A where }}} {{{ $ ghc-stage2 -prof -c A.hs Top level: Failed to load interface for ‛GHC.Integer.Type’ Perhaps you haven't installed the profiling libraries for package ‛integer-gmp’? Use -v to see a list of the files searched for. }}} I can't built module `A` without profiling libraries for `integer-gmp`, even though I don't use `integer-gmp` anywhere in the module. This happens because the `Tidy Core` pass attempts to look up the `mkInteger` name (in order to desugar integer literals) even when there are no integer literals in the module. The obvious fix is to lazily look up `mkInteger` in `Coreprep.lookupMkIntegerName`: {{{ #!diff diff --git a/compiler/coreSyn/CorePrep.lhs b/compiler/coreSyn/CorePrep.lhs index 5e0cd65..9836982 100644 --- a/compiler/coreSyn/CorePrep.lhs +++ b/compiler/coreSyn/CorePrep.lhs @@ -56,6 +56,7 @@ import Config import Data.Bits import Data.List ( mapAccumL ) import Control.Monad +import System.IO.Unsafe ( unsafeInterleaveIO ) \end{code} -- --------------------------------------------------------------------------- @@ -1119,6 +1120,7 @@ lookupMkIntegerName dflags hsc_env else if thisPackage dflags == integerPackageId then return $ panic "Can't use Integer in integer" else liftM tyThingId + $ unsafeInterleaveIO $ initTcForLookup hsc_env (tcLookupGlobal mkIntegerName) mkInitialCorePrepEnv :: DynFlags -> HscEnv -> IO CorePrepEnv }}} This way, we don't attempt to look up `mkInteger` until we actually need it, i.e. if there are integer literals that we must desugar. Relevant commits are 2ef5cd26db27543ac8664a3d18f45550d0109a8b and fdd552e0ecaa17300670a48562995040e1d6687e -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8572> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10192: Template Haskell crashes when building yesod-core package
by GHC 24 Jan '16

24 Jan '16

#10192: Template Haskell crashes when building yesod-core package -------------------------------------+------------------------------------- Reporter: DanielDiaz | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- This is the output when trying to install yesod-core in a sandbox: {{{ Configuring yesod-core-1.4.8.3... Building yesod-core-1.4.8.3... Preprocessing library yesod-core-1.4.8.3... [ 1 of 31] Compiling Yesod.Routes.TH.Types ( Yesod/Routes/TH/Types.hs, dist/dist-sandbox-d1f72a97/build/Yesod/Routes/TH/Types.o ) [ 2 of 31] Compiling Yesod.Routes.TH.Dispatch ( Yesod/Routes/TH/Dispatch.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Routes/TH/Dispatch.o ) [ 3 of 31] Compiling Yesod.Routes.Overlap ( Yesod/Routes/Overlap.hs, dist /dist-sandbox-d1f72a97/build/Yesod/Routes/Overlap.o ) [ 4 of 31] Compiling Yesod.Core.TypeCache ( Yesod/Core/TypeCache.hs, dist /dist-sandbox-d1f72a97/build/Yesod/Core/TypeCache.o ) [ 5 of 31] Compiling Yesod.Routes.Class ( Yesod/Routes/Class.hs, dist /dist-sandbox-d1f72a97/build/Yesod/Routes/Class.o ) [ 6 of 31] Compiling Yesod.Routes.TH.RenderRoute ( Yesod/Routes/TH/RenderRoute.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Routes/TH/RenderRoute.o ) [ 7 of 31] Compiling Yesod.Routes.TH.ParseRoute ( Yesod/Routes/TH/ParseRoute.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Routes/TH/ParseRoute.o ) [ 8 of 31] Compiling Yesod.Routes.TH.RouteAttrs ( Yesod/Routes/TH/RouteAttrs.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Routes/TH/RouteAttrs.o ) [ 9 of 31] Compiling Yesod.Routes.TH ( Yesod/Routes/TH.hs, dist/dist- sandbox-d1f72a97/build/Yesod/Routes/TH.o ) [10 of 31] Compiling Yesod.Routes.Parse ( Yesod/Routes/Parse.hs, dist /dist-sandbox-d1f72a97/build/Yesod/Routes/Parse.o ) [11 of 31] Compiling Paths_yesod_core ( dist/dist-sandbox- d1f72a97/build/autogen/Paths_yesod_core.hs, dist/dist-sandbox- d1f72a97/build/Paths_yesod_core.o ) [12 of 31] Compiling Yesod.Core.Internal.Util ( Yesod/Core/Internal/Util.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Core/Internal/Util.o ) [13 of 31] Compiling Yesod.Core.Types ( Yesod/Core/Types.hs, dist/dist- sandbox-d1f72a97/build/Yesod/Core/Types.o ) [14 of 31] Compiling Yesod.Core.Class.Handler ( Yesod/Core/Class/Handler.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Core/Class/Handler.o ) Yesod/Core/Class/Handler.hs:25:1: Warning: Module ‘Control.Monad.Trans.Error’ is deprecated: Use Control.Monad.Trans.Except instead Yesod/Core/Class/Handler.hs:56:11: Warning: In the use of type constructor or class ‘Error’ (imported from Control.Monad.Trans.Error): Deprecated: "Use Control.Monad.Trans.Except instead" Yesod/Core/Class/Handler.hs:56:54: Warning: In the use of type constructor or class ‘ErrorT’ (imported from Control.Monad.Trans.Error): Deprecated: "Use Control.Monad.Trans.Except instead" Yesod/Core/Class/Handler.hs:56:91: Warning: In the use of type constructor or class ‘ErrorT’ (imported from Control.Monad.Trans.Error): Deprecated: "Use Control.Monad.Trans.Except instead" Yesod/Core/Class/Handler.hs:79:11: Warning: In the use of type constructor or class ‘Error’ (imported from Control.Monad.Trans.Error): Deprecated: "Use Control.Monad.Trans.Except instead" Yesod/Core/Class/Handler.hs:79:52: Warning: In the use of type constructor or class ‘ErrorT’ (imported from Control.Monad.Trans.Error): Deprecated: "Use Control.Monad.Trans.Except instead" [15 of 31] Compiling Yesod.Core.Internal.Request ( Yesod/Core/Internal/Request.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Core/Internal/Request.o ) [16 of 31] Compiling Yesod.Core.Internal.Session ( Yesod/Core/Internal/Session.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Core/Internal/Session.o ) [17 of 31] Compiling Yesod.Core.Content ( Yesod/Core/Content.hs, dist /dist-sandbox-d1f72a97/build/Yesod/Core/Content.o ) Yesod/Core/Content.hs:227:27: Warning: In the use of ‘B.breakByte’ (imported from Data.ByteString): Deprecated: "It is an internal function and should never have been exported. Use 'break (== x)' instead. (There are rewrite rules that handle this special case of 'break'.)" Yesod/Core/Content.hs:232:36: Warning: In the use of ‘B.breakByte’ (imported from Data.ByteString): Deprecated: "It is an internal function and should never have been exported. Use 'break (== x)' instead. (There are rewrite rules that handle this special case of 'break'.)" Yesod/Core/Content.hs:235:19: Warning: In the use of ‘B.breakByte’ (imported from Data.ByteString): Deprecated: "It is an internal function and should never have been exported. Use 'break (== x)' instead. (There are rewrite rules that handle this special case of 'break'.)" [18 of 31] Compiling Yesod.Core.Handler ( Yesod/Core/Handler.hs, dist /dist-sandbox-d1f72a97/build/Yesod/Core/Handler.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.5.1.0 ... linking ... done. Loading package auto-update-0.1.2.1 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package bytestring-0.10.6.0 ... linking ... done. Loading package text-1.2.0.4 ... linking ... done. Loading package blaze-builder-0.4.0.1 ... linking ... done. Loading package hashable-1.2.3.2 ... linking ... done. Loading package case-insensitive-1.2.0.4 ... linking ... done. Loading package containers-0.5.6.3 ... linking ... done. Loading package scientific-0.3.3.8 ... linking ... done. Loading package attoparsec-0.12.1.3 ... linking ... done. Loading package http-date-0.0.6 ... linking ... done. Loading package http-types-0.8.6 ... linking ... done. Loading package appar-0.1.4 ... linking ... done. Loading package byteorder-1.0.4 ... linking ... done. Loading package time-1.5.0.1 ... linking ... done. Loading package unix-2.7.1.0 ... linking ... done. Loading package network-2.6.0.2 ... linking ... done. Loading package iproute-1.3.2 ... linking ... done. Loading package simple-sendfile-0.2.18 ... linking ... done. Loading package filepath-1.4.0.0 ... linking ... done. Loading package directory-1.2.2.0 ... linking ... done. Loading package process-1.2.3.0 ... linking ... done. Loading package random-1.1 ... linking ... done. Loading package stm-2.4.4 ... linking ... done. Loading package transformers-0.4.3.0 ... linking ... done. Loading package zlib-0.5.4.2 ... linking ... done. Loading package streaming-commons-0.1.10.0 ... linking ... done. Loading package unix-compat-0.4.1.4 ... linking ... done. Loading package unordered-containers-0.2.5.1 ... linking ... done. Loading package vault-0.3.0.4 ... linking ... done. Loading package nats-1 ... linking ... done. Loading package semigroups-0.16.2.2 ... linking ... done. Loading package void-0.7 ... linking ... done. Loading package wai-3.0.2.3 ... linking ... done. Loading package warp-3.0.10 ... linking ... done. Loading package ansi-terminal-0.6.2.1 ... linking ... done. Loading package base64-bytestring-1.0.0.1 ... linking ... done. Loading package data-default-class-0.0.1 ... linking ... done. Loading package bytestring-builder-0.10.4.1.2 ... linking ... done. Loading package fast-logger-2.3.0 ... linking ... done. Loading package transformers-compat-0.4.0.4 ... linking ... done. Loading package transformers-base-0.4.4 ... linking ... done. Loading package monad-control-1.0.0.4 ... linking ... done. Loading package lifted-base-0.2.3.6 ... linking ... done. Loading package old-locale-1.0.0.7 ... linking ... done. Loading package mtl-2.2.1 ... linking ... done. Loading package exceptions-0.8.0.2 ... linking ... done. Loading package mmorph-1.0.4 ... linking ... done. Loading package resourcet-1.1.4.1 ... linking ... done. Loading package stringsearch-0.3.6.5 ... linking ... done. Loading package easy-file-0.2.0 ... linking ... done. Loading package binary-0.7.4.0 ... linking ... done. Loading package old-time-1.1.0.3 ... linking ... done. Loading package unix-time-0.3.5 ... linking ... done. Loading package wai-logger-2.2.3 ... linking ... done. Loading package word8-0.1.2 ... linking ... done. Loading package wai-extra-3.0.4.6 ... linking ... done. Loading package dlist-0.7.1.1 ... linking ... done. Loading package syb-0.4.4 ... linking ... done. Loading package pretty-1.1.3.2 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package primitive-0.5.4.0 ... linking ... done. Loading package vector-0.10.12.2 ... linking ... done. Loading package aeson-0.8.0.2 ... linking ... done. Loading package blaze-markup-0.7.0.2 ... linking ... done. Loading package blaze-html-0.8.0.2 ... linking ... done. Loading package parsec-3.1.9 ... linking ... done. Loading package system-filepath-0.4.13.2 ... linking ... done. Loading package system-fileio-0.3.16.1 ... linking ... done. Loading package shakespeare-2.0.4.1 ... linking ... done. Loading package safe-0.3.8 ... linking ... done. Loading package path-pieces-0.2.0 ... linking ... done. Loading package mwc-random-0.13.3.0 ... linking ... done. Loading package conduit-1.2.4 ... linking ... done. Loading package conduit-extra-1.1.7.1 ... linking ... done. Loading package monad-loops-0.4.2.1 ... linking ... done. Loading package stm-chans-3.0.0.2 ... linking ... done. Loading package monad-logger-0.3.13.1 ... linking ... done. Loading package data-default-instances-base-0.0.1 ... linking ... done. Loading package data-default-instances-containers-0.0.1 ... linking ... done. Loading package data-default-instances-dlist-0.0.1 ... linking ... done. Loading package data-default-instances-old-locale-0.0.1 ... linking ... done. Loading package data-default-0.5.3 ... linking ... done. Loading package cookie-0.4.1.4 ... linking ... done. Loading package cereal-0.4.1.1 ... linking ... done. Loading package byteable-0.1.1 ... linking ... done. Loading package securemem-0.1.7 ... linking ... done. Loading package crypto-cipher-types-0.0.9 ... linking ... done. Loading package cipher-aes-0.2.10 ... linking ... done. Loading package crypto-random-0.0.9 ... linking ... done. Loading package cprng-aes-0.6.1 ... linking ... done. Loading package entropy-0.3.6 ... linking ... done. Loading package tagged-0.7.3 ... linking ... done. Loading package crypto-api-0.13.2 ... linking ... done. Loading package setenv-0.1.1.3 ... linking ... done. Loading package skein-1.0.9.2 ... linking ... done. Loading package clientsession-0.9.1.1 ... linking ... done. [19 of 31] Compiling Yesod.Core.Widget ( Yesod/Core/Widget.hs, dist/dist- sandbox-d1f72a97/build/Yesod/Core/Widget.o ) [20 of 31] Compiling Yesod.Core.Class.Breadcrumbs ( Yesod/Core/Class/Breadcrumbs.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Core/Class/Breadcrumbs.o ) [21 of 31] Compiling Yesod.Core.Class.Yesod ( Yesod/Core/Class/Yesod.hs, dist/dist-sandbox-d1f72a97/build/Yesod/Core/Class/Yesod.o ) [22 of 31] Compiling Yesod.Core.Json ( Yesod/Core/Json.hs, dist/dist- sandbox-d1f72a97/build/Yesod/Core/Json.o ) [23 of 31] Compiling Yesod.Core.Internal.Response ( Yesod/Core/Internal/Response.hs, dist/dist-sandbox- d1f72a97/build/Yesod/Core/Internal/Response.o ) [24 of 31] Compiling Yesod.Core.Internal.Run ( Yesod/Core/Internal/Run.hs, dist/dist-sandbox-d1f72a97/build/Yesod/Core/Internal/Run.o ) ByteCodeLink.lookupCE During interactive linking, GHCi couldn't find the following symbol: templatezmhaskell_LanguageziHaskellziTHziSyntax_zdfMonadQzuzdczgzgze_closure This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org }}} It's in a fresh installation of GHC-7.8.4, using cabal-install-1.22.2.0. It is worth noting that this works: {{{ cabal sandbox init cabal install yesod-core }}} But this does not: {{{ cabal sandbox init cabal install yesod-core --upgrade-dependencies --force-reinstalls }}} The context where I ran into this problem uses {{{--upgrade- dependencies}}}, and installs yesod-core as a dependency. Let me know if you need more information. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10192> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10183: Warning for redundant constraints: interaction with pattern matching
by GHC 24 Jan '16

24 Jan '16

#10183: Warning for redundant constraints: interaction with pattern matching -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Herbert gives this example: {{{ {-# LANGUAGE GADTs, DataKinds, TypeOperators, UnicodeSyntax #-} import GHC.TypeLits data List l t where Nil ∷ List 0 t (:-) ∷ t → List l t → List (l+1) t head' ∷ (1<=l) ⇒ List l t → t head' (x :- _) = x }}} We get the warning {{{ typelits1.hs:9:9: Warning: Redundant constraint: 1 <= l In the type signature for: head' ∷ (1 <= l) ⇒ List l t → t }}} But of course the warning is not redundant if we want to exclude the `(head' Nil)` case. Here's an example that doesn't depend on `TypeLits`: {{{ data T a where TT :: T True TF :: T False f :: T True -> Bool f TT = True g :: (a ~ True) => T a -> Bool g TT = True }}} Here `f` compiles fine, but `g` warns about a redundant constraint! And indeed the evidence for `(a~True)` is not used in the code for `g`. But that evidence is used to prove that the un-matched pattern `(g TF)` is unreachable. I'm not sure how to fix this. Bother. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10183> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8285: unexpected behavior with encodeFloat on large inputs
by GHC 23 Jan '16

23 Jan '16

#8285: unexpected behavior with encodeFloat on large inputs --------------------------+------------------------------------------------ Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: | Version: 7.7 Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: Incorrect result at runtime Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ benjamin scarlet discovered some unexpected behavior in encodeFloat today {{{ <bscarlet> > map (\x -> encodeFloat 1 (shiftL 1 x)) [30,31] [23:47:47] <lambdabot> [Infinity,0.0] [23:49:09] <arkeet> > encodeFloat 1 60 [23:49:10] <lambdabot> 1.152921504606847e18 [23:49:09] <arkeet> > encodeFloat 1 60 [23:49:10] <lambdabot> 1.152921504606847e18 [23:49:18] <arkeet> er. [23:50:21] <bscarlet> down in the sane range I suspect it's just fine. [23:50:43] <bscarlet> > encodeFloat 1 1000 [23:50:44] <lambdabot> 1.0715086071862673e301 [23:50:52] <bscarlet> > encodeFloat 1 10000 [23:50:53] <lambdabot> Infinity [23:50:58] <bscarlet> That's sane. [23:51:03] <arkeet> > encodeFloat 1 (2^31) [23:51:04] <lambdabot> 0.0 [23:51:13] <bscarlet> That's what I think is weird. [23:51:19] <carter> bscarlet floats are weird [23:51:23] <arkeet> > encodeFloat 1 (2^31-1) [23:51:24] <lambdabot> Infinity }}} Benjamin did a wee bit of investigation, and the problem seems to lie in https://github.com/ghc/packages-integer- gmp/blob/master/cbits/float.c#L177 in integer-gmp, where it deliberately doesn't handle the edge cases (probably worth investigating) if integer-simple has similar behavior or not -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8285> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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