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Re: [GHC] #5108: Allow unicode sub/superscript symbols in both identifiers and operators
by GHC 17 Dec '14

17 Dec '14

#5108: Allow unicode sub/superscript symbols in both identifiers and operators -------------------------------------+------------------------------------- Reporter: | Owner: mikhail.vorozhtsov | Status: infoneeded Type: feature | Milestone: 7.10.1 request | Version: 7.1 Priority: normal | Keywords: lexer unicode Component: Compiler | Architecture: Unknown/Multiple (Parser) | Difficulty: Unknown Resolution: | Blocked By: Operating System: | Related Tickets: Unknown/Multiple | Type of failure: | None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by zardoz): I also stumbled into this when trying to use the modifier letter prime (U+02B9) and related modifiers. Supporting them in identifiers would be awesome. As for operators I don’t feel strongly either way. I was just confused about modifiers not working in identifiers, because they are classified as alphanumeric in the Unicode properties. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5108#comment:14> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5144: Pattern synonyms
by GHC 17 Dec '14

17 Dec '14

#5144: Pattern synonyms -------------------------------------+------------------------------------- Reporter: simonpj | Owner: cactus Type: feature | Status: closed request | Milestone: 7.8.1 Priority: normal | Version: Component: Compiler | Keywords: PatternSynonyms Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: 8581, | 8582, 8583, 8584 | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by cactus): * keywords: pattern synonyms => PatternSynonyms -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5144#comment:50> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8584: Pattern synonym type signatures
by GHC 17 Dec '14

17 Dec '14

#8584: Pattern synonym type signatures ------------------------------------+------------------------------------- Reporter: cactus | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: 5144 | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Currently, the only way to specify a type signature for a pattern synonym is by adding type annotations to the right-hand side, like this: {{{ {-# LANGUAGE PatternSynonyms, ScopedTypeVariables #-} pattern Single x = ([x] :: [Int]) }}} Bespoke syntax for adding type signatures for pattern synonyms would probably be useful. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8584> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8968: Pattern synonyms and GADTs
by GHC 17 Dec '14

17 Dec '14

#8968: Pattern synonyms and GADTs -------------------------------------+------------------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.1-rc2 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: Unknown/Multiple | valid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- I think this one is different from #8966, but feel free to close one as duplicate if it turns out to be the same problem. The following program (using GADTs and pattern synonyms, but not kind polymorphism or data kinds) fails to check with ghc-7.8.1-rc2, but I think it should: {{{ {-# LANGUAGE GADTs, KindSignatures, PatternSynonyms #-} data X :: (* -> *) -> * -> * where Y :: f Int -> X f Int pattern C x = Y (Just x) }}} The error I get is the following: {{{ PatKind.hs:6:18: Couldn't match type ‘t’ with ‘Maybe’ ‘t’ is untouchable inside the constraints (t1 ~ Int) bound by a pattern with constructor Y :: forall (f :: * -> *). f Int -> X f Int, in a pattern synonym declaration at PatKind.hs:6:15-24 ‘t’ is a rigid type variable bound by the inferred type of C :: X t t1 x :: Int at PatKind.hs:1:1 Expected type: t Int Actual type: Maybe Int In the pattern: Just x In the pattern: Y (Just x) PatKind.hs:6:18: Could not deduce (t ~ Maybe) from the context (t1 ~ Int) bound by the type signature for (Main.$WC) :: t1 ~ Int => Int -> X t t1 at PatKind.hs:6:9 ‘t’ is a rigid type variable bound by the type signature for (Main.$WC) :: t1 ~ Int => Int -> X t t1 at PatKind.hs:1:1 Expected type: t Int Actual type: Maybe Int Relevant bindings include ($WC) :: Int -> X t t1 (bound at PatKind.hs:6:9) In the first argument of ‘Y’, namely ‘(Just x)’ In the expression: Y (Just x) }}} Note that I'd be perfectly happy to provide a type signature for the pattern synonym, but I don't know of any syntax I could use. The Wiki page at https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms mentions I might be able to write {{{ pattern C :: Int -> X Maybe Int }}} but this triggers a parse error. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8968> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9417: Pattern synonyms across modules broken in Haddock
by GHC 17 Dec '14

17 Dec '14

#9417: Pattern synonyms across modules broken in Haddock -------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Create modules as follows {{{#!hs -- PatSymDef.hs {-# Language PatternSynonyms #-} module PatSymDef where pattern Some a = Just a }}} {{{#!hs -- PatSymUse.hs {-# Language PatternSynonyms #-} module PatSymUse where import PatSymDef f :: Maybe Int -> Int f (Some a) = a f Nothing = 0 }}} Then run Haddock against them: {{{ [nix-shell:~/programming/haddock]$ ./dist/build/haddock/haddock -h /tmp/PatSymUse.hs /tmp/PatSymDef.hs -o /tmp Haddock coverage: Warning: Not found in environment: Some 50% ( 1 / 2) in 'PatSymDef' /tmp/PatSymUse.hs:9:4: Can't find interface-file declaration for data constructor Some Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error In the pattern: Some a In an equation for ‘f’: f (Some a) = a }}} Here with -ddump-if-trace: {{{ [nix-shell:~/programming/haddock]$ ./dist/build/haddock/haddock -h /tmp/PatSymUse.hs /tmp/PatSymDef.hs -o /tmp --optghc='-ddump-if-trace' Haddock coverage: Considering whether to load base:Prelude Reading interface for base:Prelude; reason: Prelude is directly imported readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/Prelude.hi readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/Prelude.dyn_hi updating EPS_ updating EPS_ Considering whether to load base:GHC.Base {- SYSTEM -} Reading interface for base:GHC.Base; reason: Loading orphan modules (base:GHC.Base) readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/GHC/Base.hi readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/GHC/Base.dyn_hi updating EPS_ Considering whether to load base:GHC.Float {- SYSTEM -} Reading interface for base:GHC.Float; reason: Loading orphan modules (base:GHC.Float) readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/GHC/Float.hi readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/GHC/Float.dyn_hi updating EPS_ Considering whether to load base:GHC.Real {- SYSTEM -} Reading interface for base:GHC.Real; reason: Loading orphan modules (base:GHC.Real) readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/GHC/Real.hi readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/GHC/Real.dyn_hi updating EPS_ loadHiBootInterface main@main:PatSymDef Considering whether to load base:Data.Maybe {- SYSTEM -} Reading interface for base:Data.Maybe; reason: The name ‘Data.Maybe.Just’ is mentioned explicitly readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/Data/Maybe.hi readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/base_DiPQ1siqG3SBjHauL3L03p/Data/Maybe.dyn_hi updating EPS_ Starting fork { Declaration for Maybe Loading decl for Data.Maybe.Maybe updating EPS_ Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} Reading interface for ghc-prim:GHC.Prim; reason: Need home interface for wired-in thing * updating EPS_ Start interface-file tc_con_decl Nothing Done interface-file tc_con_decl Data.Maybe.Nothing Start interface-file tc_con_decl Just Done interface-file tc_con_decl Data.Maybe.Just tcIfaceDecl4 Data.Maybe.Maybe } ending fork Declaration for Maybe Starting fork { Constructor Data.Maybe.Nothing } ending fork Constructor Data.Maybe.Nothing Starting fork { Constructor Data.Maybe.Just } ending fork Constructor Data.Maybe.Just ==================== Interface statistics ==================== Renamer stats: 6 interfaces read 1 type/class/variable imported, out of 776 read 0 instance decls imported, out of 42 read 0 rule decls imported, out of 53 read Need decl for PatSymDef.Some Considering whether to load main@main:PatSymDef {- SYSTEM -} Warning: Not found in environment: Some 50% ( 1 / 2) in 'PatSymDef' Considering whether to load base:Prelude Considering whether to load main@main:PatSymDef updating EPS_ Considering whether to load base:GHC.Base {- SYSTEM -} Considering whether to load base:GHC.Float {- SYSTEM -} Considering whether to load base:GHC.Real {- SYSTEM -} loadHiBootInterface main@main:PatSymUse Considering whether to load base:Data.Maybe {- SYSTEM -} Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Reading interface for ghc-prim:GHC.Types; reason: The name ‘GHC.Types.Int’ is mentioned explicitly readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/ghcpr_BE58KUgBe9ELCsPXiJ1Q2r/GHC/Types.hi readIFace /nix/store/m347lhn3g6sh2s9pv7kz68qs2jyhzphg- ghc-7.9.20140805/lib/ghc-7.9.20140805/ghcpr_BE58KUgBe9ELCsPXiJ1Q2r/GHC/Types.dyn_hi updating EPS_ Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Considering whether to load main@main:PatSymDef {- SYSTEM -} Considering whether to load base:Data.Maybe {- SYSTEM -} Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Considering whether to load ghc-prim:GHC.Types {- SYSTEM -} Need decl for PatSymDef.Some Considering whether to load main@main:PatSymDef {- SYSTEM -} /tmp/PatSymUse.hs:9:4: Can't find interface-file declaration for data constructor Some Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error In the pattern: Some a In an equation for ‘f’: f (Some a) = a }}} Originally reported to me against Haddock 2.14.3, GHC 7.8.3 and I can confirm both there and on yesterday's GHC HEAD. It'd be great if whoever is involved with pattern synonyms could take a look. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9417> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9514: Haddock panics when exporting a module with pattern synonyms
by GHC 17 Dec '14

17 Dec '14

#9514: Haddock panics when exporting a module with pattern synonyms -------------------------------------+------------------------------------- Reporter: Artyom.Kazak | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: haddock | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: Compile- Difficulty: Unknown | time crash Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- First of all: Haddock version: '''2.14.3''', GHC version: '''7.8.3'''. Create 2 files, `PatSymDef.hs` and `PatSymUse.hs`: {{{#!hs -- PatSymDef.hs {-# Language PatternSynonyms #-} module PatSymDef where pattern Pat = () }}} {{{#!hs -- PatSymUse.hs {-# Language PatternSynonyms #-} module PatSymUse (module PatSymDef) where import PatSymDef }}} Run Haddock on them: {{{ [yom@shiny tmp]$ haddock -h PatSymDef.hs PatSymUse.hs Haddock coverage: Warning: Not found in environment: PatSymDef.Pat 50% ( 1 / 2) in 'PatSymDef' haddock: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-unknown-linux): mkUsage <<details unavailable>> Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} And with `-ddump-if-trace`: {{{ [yom@shiny tmp]$ haddock -h PatSymDef.hs PatSymUse.hs --optghc='-ddump-if- trace' Haddock coverage: Considering whether to load base:Prelude Reading interface for base:Prelude; reason: Prelude is directly imported readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/Prelude.hi readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/Prelude.dyn_hi updating EPS_ updating EPS_ Considering whether to load base:GHC.Base {- SYSTEM -} Reading interface for base:GHC.Base; reason: Loading orphan modules (base:GHC.Base) readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/GHC/Base.hi readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/GHC/Base.dyn_hi updating EPS_ Considering whether to load base:GHC.Float {- SYSTEM -} Reading interface for base:GHC.Float; reason: Loading orphan modules (base:GHC.Float) readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/GHC/Float.hi readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/GHC/Float.dyn_hi updating EPS_ Considering whether to load base:GHC.Real {- SYSTEM -} Reading interface for base:GHC.Real; reason: Loading orphan modules (base:GHC.Real) readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/GHC/Real.hi readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/GHC/Real.dyn_hi updating EPS_ loadHiBootInterface main:PatSymDef Starting fork { Declaration for Monad Loading decl for GHC.Base.Monad updating EPS_ Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} Reading interface for ghc-prim:GHC.Prim; reason: Need home interface for wired-in thing * updating EPS_ Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} tc-iface-class1 Monad tc-iface-class2 Monad tc-iface-class3 Monad tc-iface-class4 Monad buildClass buildClass GHC.Base.Monad } ending fork Declaration for Monad Need decl for Control.Applicative.Applicative Considering whether to load base:Control.Applicative {- SYSTEM -} Reading interface for base:Control.Applicative; reason: Need decl for Control.Applicative.Applicative readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/Control/Applicative.hi readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/Control/Applicative.dyn_hi updating EPS_ Starting fork { Declaration for Applicative Loading decl for Control.Applicative.Applicative updating EPS_ Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} tc-iface-class1 Applicative tc-iface-class2 Applicative tc-iface-class3 Applicative tc-iface-class4 Applicative buildClass buildClass Control.Applicative.Applicative } ending fork Declaration for Applicative Need decl for Control.Monad.MonadPlus Considering whether to load base:Control.Monad {- SYSTEM -} Reading interface for base:Control.Monad; reason: Need decl for Control.Monad.MonadPlus readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/Control/Monad.hi readIFace /usr/lib/ghc-7.8.3/base-4.7.0.1/Control/Monad.dyn_hi updating EPS_ Starting fork { Declaration for MonadPlus Loading decl for Control.Monad.MonadPlus updating EPS_ Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} tc-iface-class1 MonadPlus tc-iface-class2 MonadPlus tc-iface-class3 MonadPlus tc-iface-class4 MonadPlus buildClass buildClass Control.Monad.MonadPlus } ending fork Declaration for MonadPlus Starting fork { Declaration for Alternative Loading decl for Control.Applicative.Alternative updating EPS_ Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} Considering whether to load ghc-prim:GHC.Prim {- SYSTEM -} tc-iface-class1 Alternative tc-iface-class2 Alternative tc-iface-class3 Alternative tc-iface-class4 Alternative buildClass buildClass Control.Applicative.Alternative } ending fork Declaration for Alternative ==================== Interface statistics ==================== Renamer stats: 7 interfaces read 4 type/class/variable imported, out of 1234 read 0 instance decls imported, out of 97 read 0 rule decls imported, out of 53 read Need decl for PatSymDef.Pat Considering whether to load main:PatSymDef {- SYSTEM -} Warning: Not found in environment: PatSymDef.Pat 50% ( 1 / 2) in 'PatSymDef' Considering whether to load base:Prelude Considering whether to load main:PatSymDef updating EPS_ Considering whether to load base:GHC.Base {- SYSTEM -} Considering whether to load base:GHC.Float {- SYSTEM -} Considering whether to load base:GHC.Real {- SYSTEM -} loadHiBootInterface main:PatSymUse haddock: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-unknown-linux): mkUsage <<details unavailable>> Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9514> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9705: Panic on a pattern synonym in a class
by GHC 17 Dec '14

17 Dec '14

#9705: Panic on a pattern synonym in a class -------------------------------------+------------------------------------- Reporter: monoidal | 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: Compile- Blocked By: | time crash Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- This silly code causes a panic in rnMethodBind: {{{#!hs {-# LANGUAGE PatternSynonyms #-} class C a where pattern P = () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9705> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9161: Pattern synonyms interact badly with data kinds
by GHC 17 Dec '14

17 Dec '14

#9161: Pattern synonyms interact badly with data kinds -------------------------------------------------+------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler | Version: Keywords: renamer, pattern synonyms, | 7.8.2 data kinds | Operating System: Architecture: Unknown/Multiple | Linux Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------------+------------------------- If we define a pattern `A` and use it as a type: {{{ {-# LANGUAGE PatternSynonyms, DataKinds #-} pattern A = () b :: A b = undefined }}} we get the following error: {{{ Prelude> :load tmp.XDGqzccOAV.hs [1 of 1] Compiling Main ( /tmp/tmp.XDGqzccOAV.hs, interpreted ) /tmp/tmp.XDGqzccOAV.hs:5:9: GHC internal error: ‘A’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [] In the type signature for ‘blah’: blah :: A Failed, modules loaded: none. }}} Also occurs with different arities of `A` (the arity of the pattern and type can differ) and defining it as an operator (enabling the `TypeOperators` pragma). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9161> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9226: Internal error when using equality constraint in pattern synonyms
by GHC 17 Dec '14

17 Dec '14

#9226: Internal error when using equality constraint in pattern synonyms -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler | Version: 7.8.2 Keywords: renamer, pattern | Operating System: Linux synonyms, GADTs | Type of failure: GHC rejects Architecture: x86 | valid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- While going through [http://www.andres-loeh.de/dgp2005.pdf Extensible datatypes] I had the following code: {{{ {-# LANGUAGE GADTs, PatternSynonyms, ScopedTypeVariables, Rank2Types #-} data Rep a where RUnit :: Rep () RInt :: Rep Int RChar :: Rep Char REither :: Rep a -> Rep b -> Rep (Either a b) RPair :: Rep a -> Rep b -> Rep (a, b) foo :: (Rep a, a) -> Bool foo (RUnit, ()) = True }}} And I wanted to make a pattern synonyms matching `(RUnit, ())` in `foo`, my initial attempt was: {{{ pattern PUnit1 = (RUnit, ()) }}} gives the error (`punit1.log`) while writing {{{ pattern PUnit2 = (RUnit, ()) :: (Rep (), ()) }}} compiles but can't be used in `foo`. Trying: {{{ pattern PUnit3 = (RUnit, ()) :: (a ~ ()) => (Rep a, a) }}} gives a ''GHC internal error'' (`punit3.log`). I tried various other patterns such as: {{{ pattern PUnit4 <- (RUnit, ()) pattern PUnit5 <- (RUnit, ()) :: (Rep (), ()) pattern PUnit6 <- (RUnit, ()) :: (a ~ ()) => (Rep a, a) pattern PUnit7 = (RUnit, ()) :: forall a. (a ~ ()) => (Rep a, a) pattern PUnit8 <- (RUnit, ()) :: forall a. (a ~ ()) => (Rep a, a) ... }}} None of which work. The final goal was to rewrite: {{{ eq :: Rep a -> a -> a -> Bool eq rep a b = case (rep, a, b) of (RUnit, (), ()) -> True (RInt, n1, n2) -> n1 == n2 (RChar, c1, c2) -> c1 == c2 (REither l r, Left a, Left b) -> eq l a b (REither l r, Right a, Right b) -> eq r a b (REither{}, _, _) -> False (RPair l r, (a1, a2), (b1, b2)) -> eq l a1 b1 && eq r a2 b2 }}} as something like {{{ pattern PUnit = (RUnit, ()) -- (a ~ ()) => (Rep a, a) pattern PInt n = (RInt, n) -- (a ~ Int) => (Rep a, a) -- ... eq :: Rep a -> a -> a -> Bool eq rep a b = case ((rep, a), (rep, b)) of (PUnit, PUnit) -> True (PInt n1, PInt n2) -> n1 == n2 (PChar c1, PChar c2) -> c1 == c2 (PLeft l l1, PLeft l l2) -> eq l l1 l2 (PRight r r1, PRight r r2) -> eq r r1 r2 ((REither{}, _), _) -> False (PFst l (a1, b1), PSnd r (a2, b2)) -> eq l a1 b1 && eq r a2 b2 }}} where one can avoid pattern matching against the `Rep` constructor directly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9226> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9819: Create typesafe method of obtaining dictionary types from class definitions, and constraint objects from dictionary types
by GHC 17 Dec '14

17 Dec '14

#9819: Create typesafe method of obtaining dictionary types from class definitions, and constraint objects from dictionary types -------------------------------------+------------------------------------- Reporter: spacekitteh | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Moderate (less | Type of failure: than a day) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Say I have a class like the following: {{{#!hs class IntLike a where fromInt :: Int -> a toInt :: a -> Int }}} There should be a typesafe, principled way to get the dictionary type created from buildClass in compiler/iface/BuildTyCl.lhs like such (in this hypothetical, using a type family: {{{#!hs plusN :: (IntLike a) => Int -> Dictionary (IntLike a) }}} It would be nice if the type family was injective, if it was implemented in such a way. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9819> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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