November 2017 - ghc-tickets

Re: [GHC] #7258: Compiling DynFlags is jolly slow
by GHC 20 Nov '17

20 Nov '17

#7258: Compiling DynFlags is jolly slow -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.1 Resolution: | Keywords: deriving-perf Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by tdammers): * Attachment "ghc-large-record-types.png" removed. Profile samples for W2.hs-style record types, comparing GHC performance for just the raw record type, derived Read, derived Show, and a hand- written getLine-based applicative record construction function. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7258> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14489: GHC panic from emacs haskell mode
by GHC 20 Nov '17

20 Nov '17

#14489: GHC panic from emacs haskell mode -------------------------------------+------------------------------------- Reporter: ggoetz | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 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: -------------------------------------+------------------------------------- Hello, I encountered a ghc panic while going through one of the chapters from "Haskell Programming from first principles". The following error message is reported from flycheck checker from src/Main.hs in the attached files: {{{ Suspicious state from syntax checker haskell-stack-ghc: Flycheck checker haskell-stack-ghc returned non-zero exit code 1, but its output contained no errors: [1 of 2] Compiling Morse ( [some path]/haskell_programming/ch14/morse/src/Morse.hs, /var/folders/2s/c4mvtf0x5_b4d9gf18r65wwh0000gn/T/flycheck-haskell-ghc- cache90097PyL/Morse.o ) [2 of 2] Compiling Main ( /var/folders/2s/c4mvtf0x5_b4d9gf18r65wwh0000gn/T/flycheck90097c8R/Main.hs, /var/folders/2s/c4mvtf0x5_b4d9gf18r65wwh0000gn/T/flycheck-haskell-ghc- cache90097PyL/Main.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-apple-darwin): initTc: unsolved constraints WC {wc_insol = [W] convertLine_a2Ml :: t_a2Mk[tau:1] (CHoleCan: convertLine)} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Try installing a more recent version of haskell-stack-ghc, and please open a bug report if the issue persists in the latest release. Thanks! }}} Stack upgrade reports "Skipping binary upgrade, you are already running the most recent version". I'm not entirely sure whether this should be reported or not (I can't say I know what I'm doing...), so I'm reporting it just in case. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14489> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14491: Windows build with "--enable-distro-toolchain" fails with "make install"
by GHC 20 Nov '17

20 Nov '17

#14491: Windows build with "--enable-distro-toolchain" fails with "make install" -------------------------------------+------------------------------------- Reporter: terrorjack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Keywords: make | Operating System: Windows Architecture: x86_64 | Type of failure: Installing GHC (amd64) | failed Test Case: | Blocked By: Blocking: | Related Tickets: 13792 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I'm building ghc (commit 606bbc310654fcf56fe068905bb1aca30d2f0a8a) under mingw64 shell. I ran the configure script with "--enable-distro- toolchain", and "make -j4" succeeds, yet "make install" yields the following error: {{{ ===--- building phase 0 make --no-print-directory -f ghc.mk phase=0 phase_0_builds make[1]: Nothing to be done for 'phase_0_builds'. ===--- building phase 1 make --no-print-directory -f ghc.mk phase=1 phase_1_builds make[1]: Nothing to be done for 'phase_1_builds'. ===--- building final phase make --no-print-directory -f ghc.mk phase=final install /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin" "rm" -f "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii.sh" echo "#!/bin/sh" >> /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii.sh echo 'exec "$(dirname "$0")"/ghc --interactive "$@"' >> /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii.sh chmod +x /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii.sh cp /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii.sh /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii-8.3.20171120.sh chmod +x /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghcii-8.3.20171120.sh /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include" /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/." && /usr/bin/install -c -m 644 includes/./*.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/./" && /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/rts" && /usr/bin/install -c -m 644 includes/rts/*.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/rts/" && /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/rts/prof" && /usr/bin/install -c -m 644 includes/rts/prof/*.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/rts/prof/" && /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/rts/storage" && /usr/bin/install -c -m 644 includes/rts/storage/*.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/rts/storage/" && /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/stg" && /usr/bin/install -c -m 644 includes/stg/*.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/stg/" && true /usr/bin/install -c -m 644 includes/ghcautoconf.h includes/ghcplatform.h includes/ghcversion.h includes/dist- derivedconstants/header/DerivedConstants.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/" /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include" /usr/bin/install -c -m 644 rts/dist/build/ffi.h rts/dist/build/ffitarget.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib/include/" /usr/bin/install -c -m 644 utils/hsc2hs/template-hsc.h "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/lib" "cp" driver/ghci/dist/build/tmp/ghci.exe driver/ghci/dist/build/tmp/ghci-8.3.20171120.exe /usr/bin/install -c -m 755 -d "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin" for i in utils/hp2ps/dist-install/build/tmp/hp2ps.exe driver/ghci/dist/build/tmp/ghci.exe driver/ghci/dist/build/tmp/ghci-8.3.20171120.exe driver/ghc/dist/build/tmp/ghc-8.3.20171120.exe driver/haddock/dist/build/tmp/haddock-8.3.20171120.exe utils/hsc2hs/dist- install/build/tmp/hsc2hs.exe utils/ghc-pkg/dist-install/build/tmp/ghc- pkg.exe utils/hpc/dist-install/build/tmp/hpc.exe utils/runghc/dist- install/build/tmp/runghc.exe ghc/stage2/build/tmp/ghc-stage2.exe; do \ /usr/bin/install -c -m 755 $i "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin" ; \ done "cp" /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/runghc.exe /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/runhaskell.exe "rm" -f "/C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghc.exe" "mv" -f /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin /ghc-stage2.exe /C/Users/astro/AppData/Local/Programs/stack/x86_64-windows/ghc-8.3.20171120/bin/ghc.exe make[1]: *** No rule to make target 'inplace/mingw', needed by 'install_mingw'. Stop. make: *** [Makefile:127: install] Error 2 }}} Is this a bug related to "--enable-distro-toolchain"? "inplace/mingw" rule should not exist here in the first place. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14491> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14486: Something is fishy in RTS's "max pause" GC statistic
by GHC 20 Nov '17

20 Nov '17

#14486: Something is fishy in RTS's "max pause" GC statistic -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 8.2.1 System | 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: -------------------------------------+------------------------------------- While looking into a GC issue, I found a peculiar inconsistency between the `+RTS -s` output and that from the eventlog. The `-s` output is, {{{ 13,756,939,024 bytes allocated in the heap 6,085,406,120 bytes copied during GC 182,001,080 bytes maximum residency (22 sample(s)) 753,160 bytes maximum slop 508 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 28674 colls, 28674 par 5.268s 2.949s 0.0001s 0.1016s Gen 1 22 colls, 21 par 0.004s 0.002s 0.0001s 0.0005s Parallel GC work balance: 79.36% (serial 0%, perfect 100%) TASKS: 9 (1 bound, 8 peak workers (8 total), using -N2) SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled) INIT time 0.007s ( 0.017s elapsed) MUT time 4.353s ( 2.556s elapsed) GC time 5.272s ( 2.951s elapsed) EXIT time 0.004s ( 0.072s elapsed) Total time 9.635s ( 5.596s elapsed) Alloc rate 3,160,479,659 bytes per MUT second Productivity 45.2% of total user, 47.0% of total elapsed }}} Note the "Max pause" statistic: gen0 apparently pauses for four orders of magnitude more than gen1. This seems rather hard to believe. Moreover, if I open the eventlog from the same run in threadscope, I find, ||= Generation =||= Collections =||= Par collections =||= Elapsed time =||= Avg pause =||= Max pause =|| || GC Total || 27215 || 25518 || 2.83s || 0.0001s || 0.1016s || || Gen 0 || 25504 || 25504 || 1.55s || 0.0001s || 0.0012s || || Gen 1 || 15 || 14 || 0.99s || 0.0657s || 0.1016s || Hmmmmmmmmm... -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14486> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #6084: Add stg_ap_pnnv and related call patterns
by GHC 19 Nov '17

19 Nov '17

#6084: Add stg_ap_pnnv and related call patterns -------------------------------------+------------------------------------- Reporter: SimonMeier | Owner: simonmar Type: feature request | Status: closed Priority: high | Milestone: 7.8.1 Component: Runtime System | Version: 7.7 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: 8313 Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by michalt): * cc: michalt (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6084#comment:42> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9118: Can't eta-reduce representational coercions
by GHC 19 Nov '17

19 Nov '17

#9118: Can't eta-reduce representational coercions ------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | 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: | ------------------------------------+------------------------------------- When I say {{{ import Data.Type.Coercion import Data.Coerce import Data.Proxy eta2 :: Coercible (f a) (g a) => Proxy a -> Coercion f g eta2 _ = Coercion }}} I get {{{ Could not coerce from ‘f’ to ‘g’ because ‘f’ and ‘g’ are different types. arising from a use of ‘Coercion’ from the context (Coercible (f a) (g a)) bound by the type signature for eta2 :: Coercible (f a) (g a) => Proxy a -> Coercion f g at /Users/rae/temp/Roles.hs:5:9-56 In the expression: Coercion In an equation for ‘eta2’: eta2 _ = Coercion }}} Unlike the case for #9116, this one is ''not'' expressible in Core. (At least, I don't see a way to do it.) So, to do this, we would have to update Core and then update the constraint solver. I ''do'' think this would be type safe. But, I also think it's reasonable to wait for someone with a real use case to shout before doing this. The only use case I have is to be able to do this: {{{ -- says that a's parameter is representational class Rep (a :: k1 -> k2) where co :: Coercible x y => Coercible (a x) (a x) instance Rep f => Rep (Compose f) where ... }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9118> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11392: Decide and document how semicolons are supposed to work in GHCi
by GHC 19 Nov '17

19 Nov '17

#11392: Decide and document how semicolons are supposed to work in GHCi -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: GHCi | Version: 7.10.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #10663 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently there is a fair bit of confusion surrounding the intended function of semicolons in GHCi (see #10663 and Phab:D1726), * the users guide doesn't discuss the matter at all * sometimes the content after semicolons work as expected {{{ λ> let x=2; y=5 λ> x+y 7 }}} * other times it is silently ignored (see #10663), {{{ λ> import Data.List; 684 λ> }}} * other times it works but the parser state is subtly wrong, resulting in (arguably) incorrect line numbers later in the session, {{{ λ> data Infix a b = a :@: b; infixl 4 :@: λ> a <interactive>:3:1: error: Variable not in scope: a }}} * some times the only way to accomplish a given task is with a semicolon, {{{ Prelude> data Infix a b = a :@: b; infixl 4 :@: -- this is OK, but: Prelude> data Infix a b = a :@: b Prelude> infixl 4 :@: <interactive>:12:10: error: The fixity signature for `:@:' lacks an accompanying binding (The fixity signature must be given where `:@:' is declared) }}} This inconsistency is surprising and at times frustrating. Let's decide how we want semicolons to work and stick with it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11392> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14484: GHC rejects use of mulit-param type class.
by GHC 18 Nov '17

18 Nov '17

#14484: GHC rejects use of mulit-param type class. -------------------------------------+------------------------------------- Reporter: trinithis | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 (Type checker) | Keywords: | Operating System: Windows Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In the following example, I instantiate a few small typeclasses. The last instantiation provided does not compile, despite it being virtually identical the prior instantiation. {{{#!hs {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE MultiParamTypeClasses #-} -------------------------------------------------------------------------------- class Collection collection handle | collection -> handle, handle -> collection where getHandles :: collection -> [handle] -------------------------------------------------------------------------------- data HandleX = HandleX Int data CollectionX = CollectionX [HandleX] instance Collection CollectionX HandleX where getHandles (CollectionX handles) = handles -------------------------------------------------------------------------------- newtype HandleY = HandleY HandleX newtype CollectionY = CollectionY CollectionX instance Collection CollectionY HandleY where getHandles (CollectionY collectionX) = map HandleY $ getHandles collectionX -- Good, this compiles! -------------------------------------------------------------------------------- newtype HandleZ = HandleZ HandleY newtype CollectionZ = CollectionZ CollectionY instance Collection CollectionZ HandleZ where getHandle (CollectionZ collectionY) = map HandleZ $ getHandles collectionY -- Error: `getHandle' is not a (visible) method of class `Collection' }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14484> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14481: Mutually dependent modules with orphan instances causes missing symbols with single-shot compilation
by GHC 18 Nov '17

18 Nov '17

#14481: Mutually dependent modules with orphan instances causes missing symbols with single-shot compilation -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 (Type checker) | 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: -------------------------------------+------------------------------------- Alan Zimmerman encountered this nasty bug in his Trees That Grow branch: Consider we have the following types, {{{#!hs module Types where data Expr p = Var String | App (Expr p) (Expr p) | ADecl (Decl p) data Decl p = Bind String (Expr p) }}} Now imagine that for some reason we want to define orphan instances for some class (`Show`, for instance) for these types in two separate modules. We would have: {{{#!hs -- Instances1.hs module Instances1 where import {-# SOURCE #-} Instances2 () import Types deriving instance Show (Decl p) -- Instances1.hs-boot module Instances1 where import Types instance Show (Decl p) -- Instances2.hs module Instances2 where import {-# SOURCE #-} Instances1 () import Types deriving instance Show (Expr p) -- Instances2.hs-boot module Instances2 where import Types instance Show (Expr p) }}} Now, for instance, say we have some program that uses this whole mess, {{{#!hs -- Main.hs module Main where import Types -- Use SOURCE import to ensure GHC doesn't grab dictionary from unfolding in -- interface file import {-# SOURCE #-} Instances2 main = putStrLn $ show $ (Var "hi" :: Expr Int) }}} With `--make` mode we can compile `Main.hs` with no trouble: {{{ $ ghc --make Main.hs [1 of 6] Compiling Types ( Types.hs, Types.o ) [2 of 6] Compiling Instances2[boot] ( Instances2.hs-boot, Instances2.o-boot ) [3 of 6] Compiling Main ( Main.hs, Main.o ) [4 of 6] Compiling Instances1[boot] ( Instances1.hs-boot, Instances1.o-boot ) [5 of 6] Compiling Instances2 ( Instances2.hs, Instances2.o ) [6 of 6] Compiling Instances1 ( Instances1.hs, Instances1.o ) Linking Main ... $ ./Main Var "hi" }}} However, if we instead use single-shot mode, we end up never producing object code for one of the boot DFuns, {{{ $ ghc -c Types.hs $ ghc -c Instances1.hs-boot $ ghc -c Instances2.hs $ ghc -c Instances2.hs-boot $ ghc -c Instances1.hs $ ghc -c Main.hs $ ghc -o test Types.o Instances1.o Instances2.o Main.o Main.o:s1lN_info: error: undefined reference to 'Instances2_zdfxShowExpr_closure' Main.o(.data.rel.ro+0x8): error: undefined reference to 'Instances2_zdfxShowExpr_closure' collect2: error: ld returned 1 exit status `gcc' failed in phase `Linker'. (Exit code: 1) }}} In the case of `--make` mode the symbol in question is emitted in the object code for `Instances2`. However, when we use single-shot mode the `hi-boot` file for `Instances2` doesn't exist when the `hs` file is compiled. It seems that this makes the DFun impedance matching logic in `TcRnDriver.checkBootIface'` not fire. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14481> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14255: Type-indexed type fingerprints
by GHC 18 Nov '17

18 Nov '17

#14255: Type-indexed type fingerprints -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Core | Version: 8.2.1 Libraries | Keywords: Typeable | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I have the feeling that it might well be possible to reduce the size of the trusted codebase somewhat by introducing type-indexed fingerprints. Imagine {{{#!hs data TypeRep (a :: k) where TrTyCon :: {-# UNPACK #-} !FingerprintIx a -> !TyCon -> [SomeTypeRep] -> TypeRep (a :: k) TrApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1). {-# UNPACK #-} !FingerprintIx (a b) -> TypeRep (a :: k1 -> k2) -> TypeRep (b :: k1) -> TypeRep (a b) TrFun :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (a :: TYPE r1) (b :: TYPE r2). {-# UNPACK #-} !FingerprintIx (a -> b) -> TypeRep a -> TypeRep b -> TypeRep (a -> b) }}} We could have some primitive operations like {{{#!hs mkFunFP :: FingerPrintIx a -> FingerPrintIx b -> FingerPrintIx (a -> b) mkAppFP :: FingerPrintIx (a -> b) -> FingerPrintIx a -> FingerPrintIx b eq :: FingerPrintIx a -> FingerPrintIx b -> Maybe (a :~~: b) eqE :: FingerPrintIx a -> FingerPrintIx b -> Either (a :~~: b -> c) (a :~~: b) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14255> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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