MissingH-1.3.0.1: Large utility library

Copyright | Copyright (C) 2004-2011 John Goerzen
License | BSD3
Maintainer | John Goerzen <jgoerzen@complete.org>
Stability | provisional
Portability | portable
Safe Haskell | None
Language | Haskell98

Data.Either.Utils

Description

Utilities for working with the Either data type

Synopsis

- maybeToEither :: MonadError e m => e -> Maybe a -> m a
- forceEither :: Show e => Either e a -> a
- forceEitherMsg :: Show e => String -> Either e a -> a
- eitherToMonadError :: MonadError e m => Either e a -> m a
- fromLeft :: Either a b -> a
- fromRight :: Either a b -> b
- fromEither :: Either a a -> a

# Documentation

maybeToEither

Arguments

:: MonadError e m |
=> e | (Left e) will be returned if the Maybe value is Nothing
-> Maybe a | (Right a) will be returned if this is (Just a)
-> m a |

Converts a Maybe value to an Either value, using the supplied parameter as the Left value if the Maybe is Nothing.

This function can be interpreted as:

    maybeToEither :: e -> Maybe a -> Either e a

Its definition is given as it is so that it can be used in the Error and related monads.

forceEither :: Show e => Either e a -> a

Pulls a Right value out of an Either value. If the Either value is Left, raises an exception with "error".

forceEitherMsg :: Show e => String -> Either e a -> a

Like `forceEither`, but can raise a specific message with the error.

eitherToMonadError :: MonadError e m => Either e a -> m a

Takes an either and transforms it into something of the more generic MonadError class.

fromLeft :: Either a b -> a

Take a Left to a value, crashes on a Right

fromRight :: Either a b -> b

Take a Right to a value, crashes on a Left

fromEither :: Either a a -> a

Take an Either, and return the value inside it