Haskell QuickCheck2使用ByteString？

Question

RWH书籍说要获得ByteString支持,我需要添加:

instance Arbitrary B.ByteString where
    arbitrary   = fmap B.pack arbitrary
    coarbitrary = coarbitrary . B.unpack

但是我用QuickCheck 2.4.1.1的GHC 7.2告诉我:

`coarbitrary' is not a (visible) method of class `Arbitrary'

有什么指针吗？

Answer 1

coarbitraryCoAbritary在QC 2.0中已经移动到它自己的类型类,所以只需删除等式即可coarbitrary.

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