Why doesn't Control.Monad.Trans.Writer.censor allow to convert the record type?

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Signature

censor :: Monad m => (w -> w) -> WriterT w m a -> WriterT w m a

But we could easily have a strictly more general

censor :: Functor m => (w -> w') -> WriterT w m a -> WriterT w' m a
censor = mapWriterT . fmap . second

Of course it won't work with a chunkmtl

, but is this a good reason? Or could it be performance related?

+3

haskell parametric-polymorphism monad-transformers

leftaroundabout Mar 31 17 at 15:35

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