Question

So I’m using a Grey-code generator to generate all possible bit Strings of length 6. The generator is as follows:

gray :: Integer -> String
gray n
 | n == 0 = [""]
 | n >  0 = map (++"0") (gray (n-1)) ++
            map (++"1") (reverse (gray (n-1)))

recipes = gray 6

Then, I’m attempting to get a specific bit from each of these Strings and convert that bit to an Integer. I’m doing this in the following way:

cost' :: String -> Cost
cost' r i = toInteger( ord ( r!!i ) )

Now, for some reason this isn’t working. Regardless of what ‘i’ value I use, the function cost’ will either result in 48 (if the bit in position 2 of the list is 0 –> ex. ‘100000’) or 49 (if the bit in position 2 of the list is 1 –> ex. ‘101000’).

It doesn’t make any sense to me why this is.. It’s my understanding that Strings are stored as lists in Haskell, and that to get a certain element ‘i’ from a list ‘r’ in Haskell, you execute ‘r!!i’.

Answer 1

That’s because ord returns the code point number of the character, and '0' is code point 48, '1' is code point 49. The function you want to use is digitToInt.