Lifted versions of System functions.

Lifted versions of functions provided in System.Directory, System.Environment and others. User can derive instances for EitherT, ErrorT, MaybeT, etc.

system-lifted

Lifted versions of Haskell System functions.

While haskell promotes the use of Maybe and Either as smart ways of dealing with errors, I found that the support for their Monad Transformers counter-parts is less than stellar.

While some packages like Errors simplify this, they still add a lot of boilerplate to the code.

The goal of this project started out as a way to write cleaner directory related code in either one of the error related monad transformers, namely EitherT, ErrorT or MaybeT (non-determinism and ListT are not yet supported).

This is achieved through typeclasses, and thus, by simply declaring some simple template haskell at the start of a file:

type EitherIOText       = EitherT Text

deriveSystemLiftedErrors "DisallowIOE [HardwareFault]" ''EitherIOText
deriveSystemDirectory   ''EitherIOText

One could then write code like this:

getXdgConfigFolder :: EitherT IOException IO FilePath
getXdgConfigFolder = isRW =<< getEnv "XDG_CONFIG_HOME"

Currently the System.Directory and System.Environment are fully supported, and there is partial support for System.Unix.Users.

More examples and wider System. support is planned. Contribuitions are welcomed.