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DanBurton/FromIntegralMay.hs

Created February 27, 2019 04:22
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Safe integral coercions via bounds checking
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FromIntegralMay.hs
{-# LANGUAGE ScopedTypeVariables, TypeApplications #-}
import Data.Int (Int32, Int64)
fromIntegralMay :: forall b a. (Bounded b, Integral a, Integral b) => a -> Maybe b
fromIntegralMay a | a > fromIntegral (maxBound @b) || a < fromIntegral (minBound @b) = Nothing
fromIntegralMay a = Just (fromIntegral a)
justMin = fromIntegralMay @Int32 (-2147483648 :: Int64)
justMax = fromIntegralMay @Int32 (2147483647 :: Int64)
nothingMin = fromIntegralMay @Int32 (-2147483649 :: Int64)
nothingMax = fromIntegralMay @Int32 (2147483648 :: Int64)
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