Re: Minor containers API changes

On 12/2/11 12:28 PM, wren ng thornton wrote:

On 11/30/11 7:51 AM, Felipe Almeida Lessa wrote:

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On Wed, Nov 30, 2011 at 4:54 AM, Liyang HU wrote:

...

How about using the Down/Dual/Desc/Converse/Opposite/Reverse newtype discussed in another recent thread, and providing for Data.Map:

reverse :: Map k a -> Map (Reverse k) a reverse Tip = Tip reverse (Bin n k a l r) = Bin n (Reverse k) a (reverse r) (reverse l)

(Arguably we also need reverse' :: Map (Reverse k) a -> Map k a. Hmm...)

reverse' :: Map (Reverse k) a -> Map k a reverse' = unsafeCoerce . reverse

Sorry, couldn't resist =).

As an addendum to the mapKeysAntitonic proposal, we should add the functorial rewrite rules which account for mono-/antitonicity.

{-# RULES "mapKeysAntitonic id" mapKeysAntitonic id = id

"mapKeysAntitonic f . mapKeysAntitonic g" mapKeysAntitonic f . mapKeysAntitonic g = mapKeysMonotonic (f . g)

Whoops, forgot the other two fusions: "mapKeysAntitonic f . mapKeysMonotonic g" mapKeysAntitonic f . mapKeysMonotonic g = mapKeysAntitonic (f . g) "mapKeysMonotonic f . mapKeysAntitonic g" mapKeysMonotonic f . mapKeysAntitonic g = mapKeysAntitonic (f . g) I know older GHC had an eta problem that led to the need for separate "f.g" and "f/g" forms of rules. I'm not sure whether that's still an issue or not though. -- Live well, ~wren