[Haskell-cafe] int to bin, bin to int

[Dan Weston]

I might be inclined to use data Bin = Zero | One
(or at least type Bin = Bool) to let the type system guarantee that 
you'll only ever have binary digits in your [Bin], not any old integer.

Using [Int] is an abstraction leak, inviting people to abuse the 
representation behind your back.

Rodrigo Queiro wrote:
> If you don't like explicit recursion (or points):
> 
> intToBin = map (`mod` 2) . takeWhile (>0) . iterate (`div` 2)
> 
> binToInt = foldl' (\n d -> n*2+d) 0
> or even:
> binToInt = foldl' ((+).(*2)) 0
> 
> On 27/09/2007, PR Stanley <prstanley at ntlworld.com> wrote:
>> Hi
>> intToBin :: Int -> [Int]
>> intToBin 1 = [1]
>> intToBin n = (intToBin (n`div`2)) ++ [n `mod` 2]
>>
>> binToInt :: [Integer] -> Integer
>> binToInt [] = 0
>> binToInt (x:xs) = (x*2^(length xs)) + (binToInt xs)
>> Any comments and/or criticisms on the above definitions would be appreciated.
>> Thanks , Paul
>>
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