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

Silly solution for one-liner fans:

(\d -> let fix f = let {x = f x} in x in fmap (\n -> "0123456789abcdef" !! n) (fix (\f l n -> if n == 0 then l :: [Int] else let (q, r) = quotRem n 16 in f (r:l) q) [] d)) 247

The nucleus of the one-liner is:

quotRem 247 16

For the sake of clarity, you can, alternatively, put the following in a file:

#!/usr/bin/env stack
{- stack script --resolver lts-12.1 -}
-- file: DecToHex.hs

module Main where

import System.Environment

fix :: (a -> a) -> a
fix f = let {x = f x} in x

ff :: ([Int] -> Int -> [Int]) -> [Int] -> Int -> [Int]
ff = \f l n ->
  if n == 0
  then l
  else
    let (q, r) = quotRem n 16
    in f (r:l) q

decToHex :: Int -> String
decToHex d =
  fmap (\n -> "0123456789abcdef" !! n)
  (fix ff [] d)

main :: IO ()
main =
  getArgs >>=
  putStrLn . show . decToHex . read . head

And execute the script with:

stack runghc -- DecToHex.hs 247

I used fixed-point operator just so it is an example with fixed-point operator; also because it allowed me to construct the one-liner strictly bottom-up. (Note: bottom-up development is to be discouraged.)

References: stack script syntax, Command line arguments, fix operator definition.

recursion haskell hex haskell-stack