You are better to use simple typeclasses. It depends on what you are trying to do, but when I want an open type, I use classes + type families.
2011/3/18 Stephen Tetley <stephen.tet...@gmail.com> > On 18 March 2011 13:31, Grigory Sarnitskiy <sargrig...@ya.ru> wrote: > > > Anyway, a new question arose. If I have already declared a type, can I > add new constructors to it from other modules? > > > > Maybe there are some GHC extensions to solve both these problems. > > "no can do". > > There are ways to encode extensible types (e.g the "finally tagless" > sytle), but on balance you are better to design extensibility for > functions - easy to add more functions - than make your code much more > complicated so it can be extensible for types. > > Parser combinators and pretty print combinators are great and largely > simple examples of extensibility with functions. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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