A redefinition of the Prelude's Enum class in order to render it safe.

LTS Haskell 22.23:
Stackage Nightly 2024-05-29:
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BSD-3-Clause licensed by wren gayle romano
Maintained by [email protected]
This version can be pinned in stack with:prelude-safeenum-,2087

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A redefinition of the Prelude’s Enum class in order to render it safe. That is, the Haskell Language Report defines pred, succ, fromEnum, and 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:

  • CPP
  • GeneralizedNewtypeDeriving
  • 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.