This haskell package started as an experiment to implement a Haskell-flavour
error-chain. Its result is ResultT,
a parameterised Monad which implements an extensible, type-safe error-handling.
This package is released on GitHub as an open source software, but it is not
distributed under any particular licence, and therefore is not (yet) a free
software. Hopefully, this will be changed before publishing chain to Hackage.
A typical monadic function which lives inside the ResultT monad will have a
type signature which looks like that:
function :: ('[Err1, Err2] :| err, Monad m)
=> a -> b -> ResultT msg err m c'[Err1, Err2] :| err means function may raise an error of type Err1 or
Err2 while it computes a result of type c. The computation is done within
the monad m, that is ResultT can be part of a monad stack a la
mtl. ResultT is not an alternative to mtl, as Eff can be. It is a more
flexible EitherT.
To escape the ResultT package means using the runResultT function, whose
type signature is:
runResultT :: ResultT msg '[] m a -> m arunResultT only accepts empty row of errors ('[]). This obliges you to
handle your error. The package provides several functions to that end.
This is still a big “work in progress” project. You can have a look at
this blogpost for an —already a bit out-dated— introduction to
the ResultT monad.
| Service | Status |
|---|---|
| Travis |  |
This package could not have been written without the works of other talented programmers, including (but not limited to):
- The freer and extensible-effects packages
- The open-union package
- The error-chain crate