Hello 👋 Announcing unwitch. A primitive conversion library with better safety and error messages. It can do safety on unboxed types as well. The idea is inspired by witch but removes the type class magic from it, instead it uses functions. So it’s like witchcraft without the magic! ✨

This is an example on how to use the library:

import qualified Unwitch.Convert.Double as Double
import qualified Unwitch.Convert.Int32 as Int32

spec = do
  Int32.toInt64 4 `shouldBe` 4
  Int32.toInt16 4 `shouldBe` Just 4

  Double.toInteger 5.0 `shouldBe` Right 5
  Double.toInteger 5.6 `shouldBe` Left $ RationalConversion $ DenomNotOne (5 % 6)

The type signatures indicate if a conversion is possible or needs checking, Int32.toInt16 may not fit for example.

I’ve been wanting to make this for years at this point, because we experience production bugs around simple primitive conversions. The problem is that writing a conversion library isn’t particularly fun. Thanks to some recent innovations, all I had to do was complain to other programs to write this. Which made all the difference in the world.