[chriswarbo]

> let's say that some integer must be between 10 and 100, do you use type checks for this?

Yep. In particular, I would use:

- A "wrapper" type around an unsigned byte (we don't need negatives, or a whole machine word)

- A "newtype" feature, to replace the wrapper with a Byte after type-checking (Haskell calls this "newtype"; Scala calls this "opaque type aliases").

- A private/unexported/scoped constructor, to prevent arbitrary Byte values getting wrapped

- A "smart constructor" which checks the bounds of a given Byte, returning a 'Maybe MyBoundedIntType' or some other type-checked error mechanism (Scala's 'Try[MyBoundedIntType]' works well).

- Polymorphism/overloading to call that smart constructor of various numeric types (char, int, long, signed, unsigned, etc.)

In Scala that would look something like:

    opaque type MyBoundedIntType = Char

    object MyBoundedIntType {
      def apply(c: Char): Try[MyBoundedIntType] =
        if (c >= 10 && c <= 100)
          Success(c)
        else
          Failure(new IllegalArgumentException(s"Value ${c.toInt} outside range [10, 100]"))

      def apply(i: Int ): Try[MyBoundedIntType] = Try(i.toChar).flatMap(MyBoundedIntType(_))
      def apply(l: Long): Try[MyBoundedIntType] = Try(l.toChar).flatMap(MyBoundedIntType(_))
    }

In Haskell:

    module MyModule (MyBoundedIntType(), toByte, MakeBounded(..)) where

    newtype MyBoundedIntType = MBIT { toByte :: Word8 }

    class MakeBounded t where
      mkBounded :: t -> Either String MyBoundedIntType

    instance MakeBounded Word8 where
      mkBounded b | b >= 10 && b <= 100 = Right (MBIT b)
      mkBounded b | otherwise           = Left ("Value " ++ show b ++ " not in range [10, 100]")

    instance MakeBounded Int where
      mkBounded i = toWord8 i >>= mkBounded

    instance MakeBounded Integer where
      mkBounded i = toInt i >>= mkBounded