Re: [Haskell-cafe] gathering position information lazily using traverse

Hmmmm... On Fri, Sep 10, 2010 at 6:47 PM, Jan Christiansen wrote:

 instance Applicative Proj where    pure = Proj . const    Proj f <*> Proj x = Proj (\p -> f (False:p) (x (True:p)))

(pure f) <*> Proj x === Proj (const f) <*> Proj x === Proj (\p -> (const f) (False:p) (x (True:p))) === Proj (\p -> f (x (True:p))) Proj f <*> (pure x) === Proj f <*> Proj (const x) === Proj (\p -> f (False:p) ((const x) (True:p))) === Proj (\p -> f (False:p) x))

 instance Applicative Proj where    pure x = Pure x    Pure f <*> Pure x = Pure (f x)    Pure f <*> Proj x = Proj (\p -> f (x p))    Proj f <*> Pure x = Proj (\p -> f p x)    Proj f <*> Proj x = Proj (\p -> f (False:p) (x (True:p)))

(pure f) <*> Proj x === Pure f <*> Proj x === Proj (\p -> f (x p)) (Proj f) <*> (pure x) === Proj f <*> Pure x === Proj (\p -> f p x) Was this difference intended? Cheers! =) -- Felipe.