On Mon, Jan 14, 2013 at 7:09 PM, Simon Peyton-Jones <simo...@microsoft.com>wrote:
> Friends**** > > ** ** > > I’d like to propose a way to “promote” newtypes over their enclosing > type. Here’s the writeup**** > > http://hackage.haskell.org/trac/ghc/wiki/NewtypeWrappers**** > > ** ** > > Any comments? Below is the problem statement, taken from the above page. > Have you considered the effect on types like Data.Set that use the uniqueness of typeclass instances to maintain invariants? e.g. even when we have "newtype X = X Y" coercing "Set X" to "Set Y" can produce a tree with the wrong shape for the Ord instance of Y. -- Andrea
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