Distribution.Utils.Progress

Cabal-2.0.1.0: A framework for packaging Haskell software

Safe Haskell | None
Language | Haskell2010

Distribution.Utils.Progress

Description

A progress monad, which we use to report failure and logging from otherwise pure code.

Synopsis

- data Progress step fail done
- stepProgress :: step -> Progress step fail ()
- failProgress :: fail -> Progress step fail done
- foldProgress :: (step -> a -> a) -> (fail -> a) -> (done -> a) -> Progress step fail done -> a

# Documentation

data Progress step fail done Source #

A type to represent the unfolding of an expensive long running calculation that may fail (or maybe not expensive, but complicated!) We may get intermediate steps before the final result which may be used to indicate progress and/or logging messages.

TODO: Apply Codensity to avoid left-associativity problem. See http://comonad.com/reader/2011/free-monads-for-less/ and http://blog.ezyang.com/2012/01/problem-set-the-codensity-transformation/

Instances

Monad (Progress step fail) # |
Methods (>>=) :: Progress step fail a -> (a -> Progress step fail b) -> Progress step fail b Source # (>>) :: Progress step fail a -> Progress step fail b -> Progress step fail b Source # return :: a -> Progress step fail a Source # fail :: String -> Progress step fail a Source #
Functor (Progress step fail) # |
Methods fmap :: (a -> b) -> Progress step fail a -> Progress step fail b Source # (<$) :: a -> Progress step fail b -> Progress step fail a Source #
Applicative (Progress step fail) # |
Methods pure :: a -> Progress step fail a Source # (<*>) :: Progress step fail (a -> b) -> Progress step fail a -> Progress step fail b Source # liftA2 :: (a -> b -> c) -> Progress step fail a -> Progress step fail b -> Progress step fail c Source # (*>) :: Progress step fail a -> Progress step fail b -> Progress step fail b Source # (<*) :: Progress step fail a -> Progress step fail b -> Progress step fail a Source #
Monoid fail => Alternative (Progress step fail) # |
Methods empty :: Progress step fail a Source # (<|>) :: Progress step fail a -> Progress step fail a -> Progress step fail a Source # some :: Progress step fail a -> Progress step fail [a] Source # many :: Progress step fail a -> Progress step fail [a] Source #

stepProgress :: step -> Progress step fail () Source #

Emit a step and then continue.

failProgress :: fail -> Progress step fail done Source #

Fail the computation.

foldProgress :: (step -> a -> a) -> (fail -> a) -> (done -> a) -> Progress step fail done -> a Source #

Consume a `Progress` calculation. Much like `foldr` for lists but with two base cases, one for a final result and one for failure.

Eg to convert into a simple `Either` result use:

    foldProgress (flip const) Left Right