Data.Either.Result

Result a is a wrapper of Either String a, but Result is an instance of MonadFail. A discussion about MonadFail of Either is https://gitlab.haskell.org/ghc/ghc/-/issues/12160.

Documentation

type Result = ResultT Identity

A result monad.

pattern Result :: Either String a -> Result a

Wrap Result a.

pattern Error :: String -> Result a

Error means errors and failures etc.

pattern Success :: a -> Result a

Success means successes and OKs etc.

runResult :: Result a -> Either String a

Unrap Result a.

result :: (String -> b) -> (a -> b) -> Result a -> b

Case analysis for the Result type.

Examples

>>> let s = Success 0
>>> let e = Error "critical"
>>> result ("Bad: " ++) (("OK: " ++) . show) s
"OK: 0"
>>> result ("Bad: " ++) (("OK: " ++) . show) e
"Bad: critical"

fromEither :: Either String a -> Result a

Convert Either String a to Result a.

toEither :: Result a -> Either String a

Convert Result a to Either String a.

fromSuccess :: a -> Result a -> a

Convert Result a to a with a default value.

toMonadFail :: MonadFail m => Result a -> m a

Convert Result a to MonadFail m => m a.