descript-lang-0.2.0.0: src/Core/Numeric.hs

module Core.Numeric
  ( readBinary
  , readFrac
  ) where

import Numeric
import Data.Ratio

-- | Reads a binary number (1s and 0s).
readBinary :: (Num a) => ReadS a
readBinary = readInt 2 (`elem` "01") readBit

readBit :: Char -> Int
readBit '0' = 0
readBit '1' = 1
readBit x = error $ "Expected a bit, got " ++ show x

-- | Reads a fraction - @a/b@, where @a@ and @b@ are integers.
readFrac :: ReadS Rational
readFrac str = do
  (numer, inter) <- read str
  '/' : inter' <- [dropWhile (' ' ==) inter]
  (denom, rest) <- read inter'
  pure (numer % denom, rest)