Re: [Haskell-cafe] for = flip map

Some more bikeshedding: Perhaps ffor, as in ffor = flip fmap or perhaps infixr 0 <$$> (<$$>) = flip (<$>) xs <$$> \x -> ... (cf. <**>) In both cases they should go in Data.Functor Sjoerd On Mar 28, 2012, at 11:26 PM, ezra@ezrakilty.net wrote:

I would very much like to see a standard function for "flip map" along these lines. I think it would make a lot of code more readable.

Like the OP, I use "for" in my own code. It's unfortunate that Data.Traversable takes the name with another type. Two options would be to (a) reuse the name in Data.List and force people to qualify as necessary, or (b) choose another name for "flip map".

Regarding other possible names: forall is a keyword and forAll is used by QuickCheck. One possibility would be "foreach".

Ezra

On Wed, Mar 28, 2012, at 10:19 PM, Christopher Done wrote:

...

On 28 March 2012 22:05, Matthew Steele wrote:

...

Doesn't for already exist, in Data.Traversable? Except that for = flip traverse.

Traverse doesn't fit the type of fmap, it demands an extra type constructor:

traverse :: (Traversable t,Applicative f) => (a -> f b) -> t a -> f (t b)

fmap :: Functor f => (a -> b) -> f a -> f b

Note the (a -> f b) instead of (a -> b).

E.g.

fmap :: (a -> b) -> [a] -> [b]

can't be expressed with traverse, you can only get this far:

traverse :: (a -> [b]) -> [a] -> [[b]]

Unless I'm missing something.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Sjoerd Visscher https://github.com/sjoerdvisscher/blog