On Sun, Oct 6, 2013 at 6:54 PM, Tillmann Rendel <ren...@informatik.uni-marburg.de> wrote: > Hi, > > > Ryan Newton wrote: >> >> It is very hard for me to >> see why people should be able to make their own Generic instances (that >> might lie about the structure of the type), in Safe-Haskell. > > > I guess that lying Generics instances might arise because of software > evolution. Let's say we start with an abstract data type of binary trees.
Hi, A real example exists in containers for the older Data class. Data.Sequence.Seq pretends it is a list instead of a tree: >>> gshow (S.fromList [1,2,3] S.|> 4) "(<| (1) (<| (2) (<| (3) (<| (4) (empty)))))" If there was a Generic instance for Seq, it would probably pretend to be a list for the same reasons the Data instance is that way. -- Adam _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
