Copyright | Copyright (C) 2004-2011 John Goerzen |
---|---|

License | BSD3 |

Maintainer | John Goerzen <jgoerzen@complete.org> |

Stability | provisional |

Portability | portable |

Safe Haskell | None |

Language | Haskell98 |

Utilities for working with the Either data type

- 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

:: 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 Source

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 Source

Like `forceEither`

, but can raise a specific message with the error.

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

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

fromEither :: Either a a -> a Source

Take an Either, and return the value inside it