data *(Bits b) =>* BitList b Is deprecated and soon to be removed from the language.
I fail to understand. Why not just:
data BitList b = Nil | BitList Int b (BitList b) ??
2011/10/9 Roman Beslik
I am not aware of such a library, but IMHO this code will be very simple.
data Bits b => BitList b = BitList Int {- number of used bits in the next component -} b [b] Write an isomorphism between @BitList b@ and @ListStep (BitList b)@ where data ListStep e rc = Nil | Cons e rc
On 07.10.11 17:52, Ryan Newton wrote:
Hi Cafe,
We are lucky to have a plethora of data structures out there. But it does make choosing one off hackage difficult at times. In this case I'm *not* looking for a O(1) access bit vector (Data.Vector.Unboxed seems to be the choice there), but an efficient representation for a list of bits (cons,head,tail).
Let's say that you want to represent tree indices as you walk down a binary tree. [Bool] is a simple choice, you only add to the front of the list (0/1 = Left/Right), sharing the tails. But [Bool] is quite space inefficient.
Something like [Int] would allow packing the bits more efficiently. A Lazy ByteString could amortize the space overhead even more... but in both cases there's a tiny bit of work to do in wrapping those structures for per-bit access. That's probably the right thing but I wanted to check to see if there's something else recommended, perhaps more off-the-shelf.
What about just using the Data.Bits instance of Integer? Well, presently, the setBit instance for very large integers creates a whole new integer, shifts, and xors:
http://haskell.org/ghc/docs/latest/html/libraries/base/src/Data-Bits.html#se... (I don't know if it's possible to do better. From quick googling GMP seems to use an array of "limbs" rather than a chunked list, so maybe there's no way to treat large Integers as a list and update only the front...)
Advice appreciated!
Thanks, -Ryan
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