ghc panic: varargs + sets

This program:

{-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-}

import qualified Data.Set as S

class BuildSet a b | b -> a

where buildset' :: S.Set a -> a -> b

instance Ord a => BuildSet a (S.Set a)

where buildset' s i = S.insert i s

instance Ord a => BuildSet a b => BuildSet a (a -> b)

where buildset' s i = \ i2 -> buildset' (S.insert i s) i2

buildset :: BuildSet a b => a -> b buildset = buildset' S.empty

s1 :: S.Set Integer s1 = buildset 3

s2 :: S.Set Integer s2 = buildset 1 2 3

s3 :: S.Set Integer s3 = buildset 8 4 2 1 2 4 8 18

main = do

putStrLn $ show l1 putStrLn $ show l2 putStrLn $ show l3

produces this output when compiled:

$ ghc --make test.hs [1 of 1] Compiling Main ( test.hs, test.o ) ghc: panic! (the 'impossible' happened)

(GHC version 7.4.1 for x86_64-unknown-linux):

compiler/rename/RnSource.lhs:429:14-81: Irrefutable pattern failed for pattern Data.Maybe.Just (inst_tyvars,

_,

SrcLoc.L _ cls,

_)

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

$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.4.1

Trac metadata

Trac field	Value
Version	7.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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