pharpend/exceptional

A simple Haskell type for pure code that could go wrong.

exceptional

This is a Haskell library that exists to house a type:

data Exceptional x
  = Failure String
  | Success x

It's much like Maybe, except instead of Nothing, we have Failure String.

A comparison could also be made to Either String. I made this library because I was dissatisfied with the Monad instance for Either. In this type, fail = Failure. It's rather simple.

Installing

cabal install exceptional

Or, add exceptional to the build-depends field in your .cabal file.

exceptional's Issues

Compilation issues with GHC 8.10

The fail method for Monad was removed in ghc 8.8.1, see:
https://downloads.haskell.org/~ghc/8.8.1/docs/html/users_guide/8.8.1-notes.html#base-library

Configuring library for exceptional-0.3.0.0..
Preprocessing library for exceptional-0.3.0.0..
Building library for exceptional-0.3.0.0..
[1 of 1] Compiling Control.Exceptional ( Control/Exceptional.hs, dist/build/Control/Exceptional.o, dist/build/Control/Exceptional.dyn_o )

Control/Exceptional.hs:43:3: error:
    ‘fail’ is not a (visible) method of class ‘Monad’
   |
43 |   fail = Failure
   |   ^^^^