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Prelude Hack : divide and remainder return Either Monad

More than 5 years have passed since last update.

See also
1. http://voqn.blogspot.com/2012/01/bdd-on-haskell-3-1-catch.html
2. http://voqn.blogspot.com/2012/01/bdd-on-haskell-3-2-throw-exception.html

Data/Numeric/Arith.hs
import qualified Data.Fixed as F
import Control.Exception
import Prelude hiding ( div, mod, divMod )
import qualified GHC.Real as R

divZero :: Either ArithException a
divZero = Left DivideByZero

div' :: (Real a, Integral b) => a -> a -> Either ArithException b
div' _ 0 = divZero
div' x y = Right $ F.div' x y

mod' :: Real a => a -> a -> Either ArithException a
mod' _ 0 = divZero
mod' x y = Right $ F.mod' x y

divMod' :: (Real a, Integral b) => a -> a -> Either ArithException (b, a)
divMod' = pairEither div' mod' divZero

div :: Integral a => a -> a -> Either ArithException a
div _ 0 = divZero
div x y = Right $ R.div x y

mod :: Integral a => a -> a -> Either ArithException a
mod _ 0 = divZero
mod x y = Right $ R.mod x y

divMod :: Integral a => a -> a -> Either ArithException (a, a)
divMod = pairEither div mod divZero

pairEither f g e x y = case (f x y, g x y) of
  (Right n, Right m) -> Right (n, m)
  _ -> e
VoQn
デジタルプロダクトデザイナー
http://voqn.github.io
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