GHC crashes with multiple => in instance

GHC will crash (rather than a syntax error) if you write

import Data.Array.Unboxed

newtype Vector r = Vector (UArray Int r)

instance (IArray UArray r) => (Num r) => Num (Vector r) where
  (Vector v1) + (Vector v2) = Vector $ listArray (0,0) []

This is unfortunately the smallest program I found that crashes the compiler; removing the definition of (+) yields a syntax error as expected.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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