Question

I have created this data type and function:

type Bit = Int

randomFloatList :: Int -> [Float]
randomFloatList seed = randoms (mkStdGen seed)

And I want to create a function that uses zipWith. The function has a seed as an argument that is used to the randomFloatList, if the random element is between 0 and noise then the bit is changed. I am trying to do it this way, but I am with difficulties with zipWith:

Thanks.

Answer 1

I believe you want to take a list of Bits and use a random list to decide whether to alter the original. (If not, please clarify.)

channel :: Int -> Float -> [Bit] -> [Bit]
channel seed noise xs = zipWith (alterBit noise) (randomFloatList seed) xs

Notice you didn’t need some of the brackets – you don’t need brackets for function application, just for grouping.

alterBit :: Float -> Float -> Bit -> Bit
alterBit noise random bit | random <= noise = alter bit
                          | otherwise = bit

Again, I’ve removed any reference to the list that I’m using this with – zipWith will send this function the single elements it needs out of the list of floats and bits.

I took the liberty of defining

data Bit = O | I deriving Show

and could only think of one alter function:

alter :: Bit -> Bit
alter O = I
alter I = O

Let’s test it:

> take 6 $ randomFloatList 3
[0.10321328,0.98988104,0.46191382,0.8553592,0.7980472,0.35561606]

> map (<= 0.5) $ take 6 $ randomFloatList 3
[True,False,True,False,False,True]

> channel 3 0.5 [O,O,O,O,O,O]
[I,O,I,O,O,I]

Yup, that changed the ones it should.