* Johan Tibell <johan.tib...@gmail.com> [2013-01-14 13:32:54-0800] > On Mon, Jan 14, 2013 at 1:19 PM, Simon Peyton-Jones > <simo...@microsoft.com> wrote: > > 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. > > > > > > > > Good point. I should add this. The wrapper should only work if the relevant > > data constructors are in scope; rather like GHC’s existing auto-unwrapping > > on foreign calls > > (http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi.html#ffi-newtype-io) > > I don't follow. Are you saying that adding an import, even if nothing > from that import is used, can effect if the program compiles? > > Does that mean if we ever add Data.Map.Internal that exposes the data > constructors to users who "know what they're doing" (i.e. are willing > to take it upon themselves to maintain the invariants) then code that > used to compile will stop to do so?
Now I don't follow you. Why will it stop compiling? If you define wrappers/unwrappers involving Data.Map, then they will compile if Data.Map.Internal is imported and will not compile if it isn't. Roman _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
