A redefinition of the Prelude’s
Enum class in order to render it
safe. That is, the Haskell Language Report defines
toEnum to be partial functions when the type is
Bounded. This is unacceptable. We define a new type-class hierarchy
for enumeration which is safe and also generalizes to cover types
which can only be enumerated in one direction.
This is a very simple package and should be easy to install. You should be able to use the standard:
$> cabal install prelude-safeenum
An attempt has been made to keep this library portable; however, it does rely on a few language extensions. All the required language extensions are:
- MagicHash - only for GHC
- Trustworthy - only for GHC >= 7.1
The GeneralizedNewtypeDeriving extension is used for brevity in Data.Number.CalkinWilf. If you’d like to use this package with a compiler that does not support that extension, contact the maintainer and it can be removed.
This package is only “Trustworthy” rather than “Safe” for two reasons: (1) Data.Number.CalkinWilf uses GeneralizedNewtypeDeriving, and (2) Prelude.SafeEnum imports GHC.Exts for build/foldr fusion and for the Char instances.