2009/11/3 Neil Brown
Hi,
I was thinking about some of my code today, and I realised that where I have an arrow in my code, A b c, the type (A b) is also a functor. The definition is (see http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Arrow.htm...):
fmap = (^<<) -- Or, in long form: fmap f x = arr f <<< x
Out of curiosity, and since this is a typical haskell-cafe question, does this definition of fmap hold for all arrows?
And is there a wiki page somewhere that has a table of all of these Haskell type-classes (Functor, Monad, Category, Arrow, Applicative and so on), and says that if you are an instance of class A you must have some corresponding instance of B? (e.g. all Monads are Functors and Applicatives) I'm fairly certain my arrow isn't a Monad or Applicative, although of course it must be a Category, given the type-class dependency, but it would be nice when using one of these things to see what other instances you should automatically supply.
What about the Typeclassopedia (http://haskell.org/sitewiki/images/8/85/TMR-Issue13.pdf)?
Thanks,
Neil. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
-- Eugene Kirpichov Web IR developer, market.yandex.ru