How to print integer literals in binary or hex in haskell?

Question

How to print integer literals in binary or hex in haskell?

printBinary 5 => \"0101\"

printHex 5 => \"05\"

Which libraries/functions allo

Answer 1

You could define your own recursive functions like:

import Data.Char (digitToInt)
import Data.Char (intToDigit)

-- generic function from base to decimal
toNum :: [Char] -> Int -> (Char -> Int) -> Int
toNum [] base map = 0
toNum s  base map = base * toNum (init(s)) base map + map(last(s))

-- generic function from decimal to base k
toKBaseNum :: Int -> Int -> (Int -> Char) -> [Char]
toKBaseNum x base map | x < base  = [map x]
                      | otherwise = toKBaseNum (x `div` base) base map ++ [map(x `mod` base)]


-- mapping function for hex to decimal
mapHexToDec :: Char -> Int
mapHexToDec x | x == 'A' = 10
              | x == 'B' = 11
              | x == 'C' = 12
              | x == 'D' = 13
              | x == 'E' = 14
              | x == 'F' = 15
              | otherwise = digitToInt(x) :: Int

-- map decimal to hex
mapDecToHex :: Int -> Char
mapDecToHex x | x < 10 = intToDigit(x)
              | x == 10 = 'A'
              | x == 11 = 'B'
              | x == 12 = 'C'
              | x == 13 = 'D'
              | x == 14 = 'E'
              | x == 15 = 'F'

-- hex to decimal
hexToDec :: String -> Int
hexToDec [] = 0
hexToDec s = toNum s 16 mapHexToDec

-- binary to decimal
binToDec :: String -> Int
binToDec [] = 0
binToDec s  = toNum s 2 (\x -> if x == '0' then 0 else 1)

-- decimal to binary
decToBin :: Int -> String
decToBin x = toKBaseNum x 2 (\x -> if x == 1 then '1' else '0')

-- decimal to hex
decToHex :: Int -> String
decToHex x = toKBaseNum x 16 mapDecToHex

Explanation: As you can see, the toNum function converts a k-based value to decimal, using the given base and a mapping function. The mapping function will map special characters to a decimal value (for ex. A=10, B=11, ... in hex). For binary mapping you could also use a lambda expression like you see in binToDec.

Whereas the toKBaseVal function is the opposite, converting a decimal to a k-based value. Again we need a mapping function which does the opposite: from a decimal to the corresponding special character of the k-based value.

As a test you can type:

binToDec(decToBin 7) = 7

Suppose you want to convert from decimal to octal:

-- decimal to octal
decToOct :: Int -> String
decToOct x = toKBaseNum x 8 (\x -> intToDigit(x))

Again, I use just a lambda expression, because the mapping is simple: just int to digit.

Hope that helps! Good programming!