core lint error with arrow notation and GADTs

The following code panics GHC (with 7.0.3, 7.2 and 7.4.0.20111219):

{-# LANGUAGE Arrows, GADTs #-}
import Control.Arrow

data Value a where BoolVal :: Value Bool

class ArrowInit f where
    arrif :: f b -> ()

instance ArrowInit Value where
    arrif = proc BoolVal -> returnA -< ()
    -- arrif = arr (\BoolVal -> ())

I am attaching the -dcore-lint from 7.4.

Trac metadata

Trac field	Value
Version	7.4.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	ben@moseley.name, benjamin.moseley@barclayscapital.com
Operating system	MacOS X
Architecture	x86

changed weight to 5

added GADTs Tbug Trac import labels

Attached file arrow-gadt-panic.txt (download).

Core Lint output

Attached file Test3.hs ($655).

Source file

changed title from Panic with Arrow Notation and GADTs to core lint error with arrow notation and GADTs

Simplified version, avoiding classes:

{-# LANGUAGE Arrows, GADTs #-}
module ArrowBug5777 where

import Control.Arrow

data Value a where BoolVal :: Value Bool

arrif :: Value Bool -> ()
arrif = proc BoolVal -> returnA -< ()

The workaround is to move the GADT data constructor out of the 'proc' pattern and into a 'let':

data Value a where BoolVal :: Int -> Value Bool

arrif :: Value Bool -> Int
arrif = proc x -> do
          let BoolVal i = x
          returnA -< i

changed milestone to %7.4.2

changed milestone to %7.4.3

mentioned in issue #7071 (closed)

changed milestone to %7.6.2

This also happens on GHC 7.4.2 x86_64.

$ ghc --make Test3.hs 
[1 of 1] Compiling Main             ( Test3.hs, Test3.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.2 for x86_64-apple-darwin):
	cgLookupPanic (probably invalid Core; try -dcore-lint)
    ( $dArrow{v amL} [lid] :: base:Control.Arrow.Arrow{tc r4n}
                                ghc-prim:GHC.Prim.(->){(w) tc 3D} )
    static binds for:
    local binds for:
    ( main:Main.arrif{v rci} [gid[ClassOp]] :: forall (( f{tv acm} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d}
                                                                           -> ghc-prim:GHC.Prim.*{(w) tc 34d} ) :: ghc-prim:GHC.Prim.*{(w) tc 34d}
                                                                                                                   -> ghc-prim:GHC.Prim.*{(w) tc 34d}).
                                               main:Main.ArrowInit{tc rch}
                                                 ( f{tv acm} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d}
                                                                     -> ghc-prim:GHC.Prim.*{(w) tc 34d} ) =>
                                               forall ( b{tv acn} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d} ).
                                               ( f{tv acm} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d}
                                                                   -> ghc-prim:GHC.Prim.*{(w) tc 34d} ) ( b{tv acn} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )
                                               -> ghc-prim:GHC.Tuple.(){(w) tc 40} )
    ( main:Main.$WBoolVal{v rcH} [gid[DataConWrapper]] :: main:Main.Value{tc rcj}
                                                            ghc-prim:GHC.Types.Bool{(w) tc 3c} )

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Trac metadata

Trac field	Value
Version	7.4.1-rc1 → 7.4.2
Architecture	x86 → Unknown/Multiple

Ross, do you feel able to help with this. I have no clue.

Trac metadata

Trac field	Value
CC	abcz2.uprola@gmail.com, ben@moseley.name, benjamin.moseley@barclayscapital.com → abcz2.uprola@gmail.com, ben@moseley.name, benjamin.moseley@barclayscapital.com, ross

assigned to @trac-ross

I'll put it on my list, but first priority is ArrForm (#5267/#5609 (closed)), followed by infixr (#5333 (closed)), with this and #344 (closed) as the lowest.

mentioned in commit c3ad38d7

changed milestone to %7.10.1

Moving to 7.10.1.

Bug still present in HEAD (ghc-7.9.20141125).

Trac metadata

Trac field	Value
Component	Compiler → Compiler (Type checker)
Operating system	MacOS X → Unknown/Multiple

removed milestone

Moving to 7.12.1 milestone; if you feel this is an error and should be addressed sooner, please move it back to the 7.10.1 milestone.

mentioned in issue #9985 (closed)

changed milestone to %8.0.1

Milestone renamed

added Arrows label and removed GADTs label

mentioned in issue #13547

Trac metadata

Trac field	Value
Related	- → #13547

mentioned in issue #15175 (closed)

Trac metadata

Trac field	Value
Related	#13547 → #13547, #15175 (closed)

added GADTs label

added compiler crash label

added Pnormal label

mentioned in issue #18950 (closed)

mentioned in commit 4b574938

mentioned in merge request !4957 (closed)

mentioned in commit f92dc532

closed with commit 18e53386

mentioned in commit 18e53386