Dec to BaseN and back

BaseChange.hs

module BaseChange where

import           Data.Foldable       (foldl')

-- Turns a base 10 number into a list representation in another base
-- based on the zero and digit representation you pass in
-- :: Integral -> zero -> [digits] -> [representation]
decToBaseN :: Integral a => a -> b -> [b] -> [b]
decToBaseN i zero digits = if base == 0 then [] else go i []
  where
    base = fromIntegral $ length digits
    go 0 [] = [zero]
    go 0 acc = acc
    go curr acc =
      let (q, r) = quotRem curr base
      in go q ((digits !! fromIntegral r) : acc)
      
-- Given a base, a conversion from a to Num a, and a list of a's representing a number
-- returns the base 10 representation of that number
baseNToDec :: Num i => i -> (a -> i) -> [a] -> i
baseNToDec base toInt = foldl' (\acc n -> base * acc + toInt n ) 0