[Haskell-cafe] Generalized Newtype Deriving not allowed in Safe Haskell

Omari Norman omari at smileystation.com
Thu Apr 9 01:43:34 UTC 2015

When compiling code with Generalized Newtype Deriving and the -fwarn-unsafe
flag, I get

-XGeneralizedNewtypeDeriving is not allowed in Safe Haskell

This happens both in GHC 7.8 and GHC 7.10.

I thought I remembered reading somewhere that GNTD is now part of the safe
language?  The GHC manual used to state that GNTD is not allowed in Safe


But this language on GNTD not being part of the safe language was removed
in the 7.8 manual:


The GHC release notes don't say anything about this one way or the other.
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