March 2017 - ghc-tickets

[GHC] #13328: Foldable, Functor, and Traversable deriving handle phantom types badly
by GHC 30 Mar '17

30 Mar '17

#13328: Foldable, Functor, and Traversable deriving handle phantom types badly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.1 Keywords: deriving-perf | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Suppose we have {{{#!hs data Phantom a = Z | S (Phantom a) }}} We'd like to get something like {{{#!hs foldMap _ _ = mempty fmap = coerce traverse _ m = pure (coerce m) }}} But instead we actually pattern match all the way down! Basically, we want to treat "has a phantom role" and "does not occur" similarly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13328> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13494: ASSERT failed in compiler/typecheck/TcErrors.hs
by GHC 30 Mar '17

30 Mar '17

#13494: ASSERT failed in compiler/typecheck/TcErrors.hs -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 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: -------------------------------------+------------------------------------- One of the commits in the range https://github.com/ghc/ghc/compare/a6675a93efe7...de4723fd6d97 which were commited by SPJ, broke running the test suite with a `-DDEBUG` compiler: {{{ +++ /tmp/ghctest-sw9832/test spaces/./indexed- types/should_fail/T2627b.run/T2627b.comp.stderr.normalised 2017-03-27 16:28:10.448037112 +0000 @@ -1,13 +1,17 @@ +ghc: panic! (the 'impossible' happened) + (GHC version 8.3.20170327 for x86_64-unknown-linux): + ASSERT failed! + b0_a1gy[tau:4] + Call stack: + CallStack (from HasCallStack): + prettyCurrentCallStack, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/TcErrors.hs:<line>:<column> in <package-id>:TcErrors + Call stack: + CallStack (from HasCallStack): + prettyCurrentCallStack, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + pprPanic, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/TcErrors.hs:<line>:<column> in <package-id>:TcErrors -T2627b.hs:20:24: - Couldn't match type â€˜b0â€™ with â€˜Dual (Dual b0)â€™ - arising from a use of â€˜connâ€™ - â€˜b0â€™ is untouchable - inside the constraints: b ~ W e f - bound by a pattern with constructor: - Wr :: forall e f. e -> Comm f -> Comm (W e f), - in an equation for â€˜connâ€™ - at T2627b.hs:20:14-19 - In the expression: conn undefined undefined - In an equation for â€˜connâ€™: - conn (Rd k) (Wr a r) = conn undefined undefined +Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} See https://s3.amazonaws.com/archive.travis-ci.org/jobs/215578687/log.txt for a full log. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13494> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13446: Deferred type error sneaks in with -fno-defer-type-errors enabled
by GHC 30 Mar '17

30 Mar '17

#13446: Deferred type error sneaks in with -fno-defer-type-errors enabled -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a very perplexing bug that MitchellSalad discovered and advertised in [https://www.reddit.com/r/haskell/comments/604mze/deferred_type_errors_witho… this Reddit post]. Consider this code: {{{#!hs {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# OPTIONS_GHC -fno-defer-type-errors #-} module Main where import Data.Coerce (Coercible) import GHC.Exts (Constraint) import GHC.TypeLits (Symbol) data Dict :: Constraint -> * where Dict :: a => Dict a infixr 9 :- newtype a :- b = Sub (a => Dict b) instance a => Show (a :- b) where showsPrec d (Sub Dict) = showParen (d > 10) $ showString "Sub Dict" class Lifting p f where lifting :: p a :- p (f a) data Blah a = Blah newtype J (a :: JType) = J (Blah (J a)) newtype JComparable a = JComparable (J (T (JTy a))) instance Lifting JReference JComparable where lifting = Sub 'a' class (Coercible a (J (JTy a))) => JReference a where type JTy a :: JType type T a = 'Generic ('Iface "java.lang.Comparable") '[a] data JType = Class Symbol | Generic JType [JType] | Iface Symbol type JObject = J (Class "java.lang.Object") instance JReference JObject where type JTy JObject = 'Class "java.lang.Object" main :: IO () main = print (lifting :: JReference JObject :- JReference (JComparable JObject)) }}} There are three concerning things about this: 1. Look at the line `lifting = Sub 'a'`. That's obviously bogus, as `Char`s are not `Dict`s! Yet GHC 8.0.2 and HEAD readily typecheck this code without warnings. 2. So now that we seem to have circumvented type safety, what happens if we actually try to //run// code which uses this bogus `Lifting` instance? Something truly bizarre, that's what: {{{ $ /opt/ghc/8.0.2/bin/ghci Bug.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Ok, modules loaded: Main. λ> main *** Exception: Bug.hs:34:17: error: • Couldn't match expected type ‘Dict (JReference (JComparable a))’ with actual type ‘Char’ • In the first argument of ‘Sub’, namely ‘'a'’ In the expression: Sub 'a' In an equation for ‘lifting’: lifting = Sub 'a' • Relevant bindings include lifting :: JReference a :- JReference (JComparable a) (bound at Bug.hs:34:3) (deferred type error) }}} Somehow, we managed to defer a type mismatch between `Char` and `Dict`. All while `-fno-defer-type-errors` is enabled! 3. Worst of all, this is a regression from GHC 8.0.1, as it will actually detect the type mismatch at compile-time: {{{ $ /opt/ghc/8.0.1/bin/ghci Bug.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:34:17: error: • Couldn't match expected type ‘Dict (JReference (JComparable a))’ with actual type ‘Char’ • In the first argument of ‘Sub’, namely ‘'a'’ In the expression: Sub 'a' In an equation for ‘lifting’: lifting = Sub 'a' • Relevant bindings include lifting :: JReference a :- JReference (JComparable a) (bound at Bug.hs:34:3) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13446> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13410: GHC HEAD regression: Template variable unbound in rewrite rule
by GHC 30 Mar '17

30 Mar '17

#13410: GHC HEAD regression: Template variable unbound in rewrite rule -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `hybrid-vectors-0.2.1` currently fails to build with GHC HEAD. I've attached a minimized repro file with no dependencies (it's 410 lines long, since I had to copy-paste a lot of code from `vector` in order to reproduce this). The attached file builds on GHC 7.10.3 and 8.0.2, but fails on GHC HEAD with this panic: {{{ $ ~/Software/ghc2/inplace/bin/ghc-stage2 -O2 -fforce-recomp Bug.hs [1 of 1] Compiling Data.Vector.Hybrid.Internal ( Bug.hs, Bug.o ) Bug.hs:389:10: warning: [-Wmissing-methods] • No explicit implementation for ‘gmbasicOverlaps’, ‘gmbasicInitialize’, and ‘gmbasicUnsafeRead’ • In the instance declaration for ‘GMVector (MVector u v) (a, b)’ | 389 | instance (GMVector u a, GMVector v b) => GMVector (MVector u v) (a, b) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Bug.hs:407:10: warning: [-Wmissing-methods] • No explicit implementation for ‘gbasicUnsafeFreeze’, ‘gbasicUnsafeThaw’, ‘gbasicLength’, ‘gbasicUnsafeSlice’, and ‘gbasicUnsafeIndexM’ • In the instance declaration for ‘GVector (Vector u v) (a, b)’ | 407 | instance (GVector u a, GVector v b) => GVector (Vector u v) (a, b) where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.3.20170310 for x86_64-unknown-linux): Template variable unbound in rewrite rule Variable: sc_s8FV Rule "SC:$j0" Rule bndrs: [sc_s8FV, sc_s8FW, sc_s8FX, sg_s8FY, sc_s8FU] LHS args: [sc_s8FU, (MV @ (GMutable u_a4oM) @ (GMutable v_a4oO) @ (PrimState (ST RealWorld)) @ (a_a4oN, b_a4oP) @ a_a4oN @ b_a4oP @~ (<(a_a4oN, b_a4oP)>_N :: ((a_a4oN, b_a4oP) :: *) ~# ((a_a4oN, b_a4oP) :: *)) sc_s8FW sc_s8FX) `cast` (sg_s8FY :: (MVector (GMutable u_a4oM) (GMutable v_a4oO) (PrimState (ST RealWorld)) (a_a4oN, b_a4oP) :: *) ~R# (GMutable (Vector u_a4oM v_a4oO) (PrimState (ST RealWorld)) c_a4oQ :: *))] Actual args: [sc_s8FS, wild_X3x `cast` (Sub (Sym (D:R:GMutableVector[0] <u_a4oM>_N <v_a4oO>_N)) <PrimState (ST RealWorld)>_N (Sym cobox_a4Gz) :: (MVector (GMutable u_a4oM) (GMutable v_a4oO) (PrimState (ST RealWorld)) (a_a4oN, b_a4oP) :: *) ~R# (GMutable (Vector u_a4oM v_a4oO) (PrimState (ST RealWorld)) c_a4oQ :: *))] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1191:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1195:37 in ghc:Outputable pprPanic, called at compiler/specialise/Rules.hs:579:19 in ghc:Rules }}} Some important things to note: * `-O2` is required to trigger this bug; using `-O1` or below works fine. * The problematic code is the `Read (Vector u v c)` instance at the very bottom. In particular, commenting out the last line `readPrec = greadPrec` makes the panic go away. * Moreover, there's a particular `INLINE` pragma in the `GMVector (MVector u v) (a, b)` instance that is critical to triggering the panic (it's on line 394; I've added a comment `Removing this INLINE pragma makes it compile` above it). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13410> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13441: Type inference failure in bidirectional pattern synonym and GADT pattern match
by GHC 30 Mar '17

30 Mar '17

#13441: Type inference failure in bidirectional pattern synonym and GADT pattern match -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In my musings in preparation toward teaching my undergrads about GADTs, I tried defining the usual old `Vec` in terms of `FList`s (definition below) and pattern synonyms. Here is the code: {{{ {-# LANGUAGE ScopedTypeVariables, PatternSynonyms, DataKinds, PolyKinds, GADTs, TypeOperators, TypeFamilies #-} module VecFList where import Data.Functor.Identity data FList f xs where FNil :: FList f '[] (:@) :: f x -> FList f xs -> FList f (x ': xs) data Nat = Zero | Succ Nat type family Length (xs :: [k]) :: Nat where Length '[] = Zero Length (_ ': xs) = Succ (Length xs) type family Replicate (n :: Nat) (x :: a) = (r :: [a]) where Replicate Zero _ = '[] Replicate (Succ n) x = x ': Replicate n x type Vec n a = FList Identity (Replicate n a) pattern Nil :: forall n a. n ~ Length (Replicate n a) => n ~ Zero => Vec n a pattern Nil = FNil pattern (:>) :: forall n a. n ~ Length (Replicate n a) => forall m. n ~ Succ m => a -> Vec m a -> Vec n a pattern x :> xs <- Identity x :@ xs where x :> xs = Identity x :@ xs }}} This fails with {{{ /Users/rae/temp/Bug.hs:30:34: error: • Could not deduce: m0 ~ Length xs arising from the "provided" constraints claimed by the signature of ‘:>’ from the context: n ~ Length (Replicate n a) bound by the type signature of pattern synonym ‘:>’ at /Users/rae/temp/Bug.hs:30:11-12 • In the declaration for pattern synonym ‘:>’ • Relevant bindings include xs :: FList Identity xs (bound at /Users/rae/temp/Bug.hs:30:34) }}} If I comment out the last two lines (the "explicitly bidirectional" part), compilation succeeds, even though the reported error is on the first line of the `:>` pattern synonym definition (the pattern part). Also, the following separate declaration compiles without incident: {{{ (>>>) :: forall n a. n ~ Length (Replicate n a) => forall m. n ~ Succ m => a -> Vec m a -> Vec n a x >>> xs = Identity x :@ xs }}} I believe the original program should compile, and should continue to compile if I replace the `<-` in the patsyn definition with `=`. For the curious: I tried putting an injectivity annotation on `Replicate` to avoid those `n ~ Length (Replicate n a)` constraints, but type family injectivity just isn't strong enough. Also, I'm not at all sure this definition is any use. But the behavior I report above shouldn't happen, regardless. Reproducible in HEAD. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13441> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13489: openTempFile fails when the template parameter contain a path separator
by GHC 29 Mar '17

29 Mar '17

#13489: openTempFile fails when the template parameter contain a path separator -------------------------------------+------------------------------------- Reporter: harendra | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 8.0.1 libraries/base | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If the template string contains a path separator, for example "a/b" then openTempFile just fails with a message which does not even indicate what the problem might be. It displays the following message: {{{ mod: /tmp/: openTempFile: does not exist (No such file or directory) }}} It can either provide a better error message, saying that path separator is not allowed or if it is legal to allow a path separator then it should create that path in the temp dir. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13489> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5654: Profiling semantics bug
by GHC 29 Mar '17

29 Mar '17

#5654: Profiling semantics bug -------------------------------------+------------------------------------- Reporter: simonmar | Owner: (none) Type: bug | Status: closed Priority: low | Milestone: 8.2.1 Component: Profiling | Version: 7.2.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | profiling/should_run/scc004 Blocked By: | Blocking: Related Tickets: #10007 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed Comment: Reverted reverting commits on `ghc-8.2` and merged fix to #13433. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5654#comment:24> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13433: Segmentation faults in profiled way
by GHC 29 Mar '17

29 Mar '17

#13433: Segmentation faults in profiled way -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.1 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: -------------------------------------+------------------------------------- It seems that profiling has regressed sometime between GHC 8.0 and 8.2. A few times since September I have noticed that profiled programs (in particular, GHC itself built with profiling enabled) seem to segmentation fault. This most recent case was produced by building commit 6ebfbdfb64cb8bb5c2ddaf2ad3ad350755c5eb2b with the following in `build.mk`, {{{ BuildFlavour = prof define add_mods_flag = $(foreach mod,$(2),$(eval $(basename $(mod))_HC_OPTS += $(1))) endef $(call add_mods_flag,-fprof-auto,$(wildcard compiler/typecheck/*.hs)) STRIP_CMD = : }}} and using the resulting stage2 compiler to bootstrap the same commit. Eventually the build will fail with a segmentation fault. Unfortunately it seems the crash isn't entirely reproducible. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13433> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13491: UNIQUE_BITS is not crosscompiler-friendly
by GHC 29 Mar '17

29 Mar '17

#13491: UNIQUE_BITS is not crosscompiler-friendly -------------------------------------+------------------------------------- Reporter: slyfox | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- Things break when I try to build crosscompiler from 32-bit system to 64-bit system. For example i386-linux -> powerpc64-linux: {{{ $ ./configure --target=powerpc64-unknown-linux-gnu --with-system-libffi --with-libffi-includes=/usr/lib/libffi-3.2.1/include/ $ make "inplace/bin/ghc-stage1" -static -H32m -O -optc-I/usr/lib/libffi-3.2.1/include -Wall -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist- ghcconstants/header -Irts -Irts/dist/build -DCOMPILING_RTS -this-unit-id rts -dcmm-lint -i -irts -irts/dist/build -Irts/dist/build -irts/dist/build/./autogen -Irts/dist/build/./autogen -O2 -Wno ncanonical-monad-instances -c rts/StgStartup.cmm -o rts/dist/build/StgStartup.o /tmp/ghc19687_0/ghc_4.s: Assembler messages: /tmp/ghc19687_0/ghc_4.s:11:0: error: Error: unknown pseudo-op: `.l' | 11 | .L�4: | ^ }}} The problem here comes from definition of `UNIQUE_BITS`: {{{#!hs # cat compiler/Unique.h #include "../includes/MachDeps.h" #define UNIQUE_BITS (WORD_SIZE_IN_BITS - 8) }}} Here `WORD_SIZE_IN_BITS` is a target platform size (64) while `stage1` is still running on host platform (32). As a result uniques truncate down to zero: {{{#!hs compiler/basicTypes/Unique.hs: tag = ord c `shiftL` UNIQUE_BITS compiler/basicTypes/Unique.hs: tag = chr (u `shiftR` UNIQUE_BITS) }}} As we operate on host '''Int'''s we could use the following: {{{#!hs #define UNIQUE_BITS sizeof(HsInt) * 8 -- C code #define UNIQUE_BITS (finiteBitSize (undefined :: Int) * 8) -- Haskell code }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13491> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8501: Improve error message when using rec/mdo keyword without RecursiveDo extention.
by GHC 29 Mar '17

29 Mar '17

#8501: Improve error message when using rec/mdo keyword without RecursiveDo extention. -------------------------------------+------------------------------------- Reporter: shelarcy | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Parser) | 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: #3968 | -------------------------------------+------------------------------------- GHC shows unhelpful error message when using rec keyword and/or mdo keyword without RecursiveDo extention. {{{ module NoRecursiveDo where foo = do rec str <- return "foo" putStrLn str }}} {{{ $ ghc -c NoRecursiveDo.hs NoRecursiveDo1.hs:4:5: Parse error in pattern: rec }}} {{{ module NoRecursiveDo2 where bar = mdo str <- return "bar" putStrLn str }}} {{{ $ ghc -c NoRecursiveDo2.hs NoRecursiveDo2.hs:4:9: parse error on input `<-' }}} {{{ module NoRecursiveDo3 where baz = mdo putStrLn "baz" }}} {{{ $ ghc -c NoRecursiveDo3.hs NoRecursiveDo3.hs:3:7: Not in scope: `mdo' Perhaps you meant `mod' (imported from Prelude) }}} I think that GHC should suggest to use RecursiveDo extention when using mdo/rec keyword. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8501> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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