Copyright | Travis Whitaker 2019 |
---|---|

License | MIT |

Maintainer | pi.boy.travis@gmail.com |

Stability | Provisional |

Portability | Portable |

Safe Haskell | Safe |

Language | Haskell2010 |

See http://programmable.computer/compatible.hs for a full exposition and worked examples.

## Synopsis

- class Compat a where
- type Pred a :: *
- type CompatConstraint a :: * -> Constraint
- type CompatF a :: * -> *
- migrate :: Pred a -> CompatF a a
- continue :: Proxy a -> Maybe (Dict (Compat (Pred a), CompatConstraint a (Pred a), CompatConstraint a ~ CompatConstraint (Pred a), CompatF a ~ CompatF (Pred a)))

- getCompatible :: forall a. (Compat a, CompatConstraint a a, Alternative (CompatF a), Monad (CompatF a)) => (forall c. (Compat c, CompatConstraint a c) => CompatF a c) -> CompatF a a

# Documentation

A class for backwards-compatible data.

The predecessor for this type, i.e. the type for the data schema
directly preceeding `a`

.

type CompatConstraint a :: * -> Constraint Source #

Any additional constraints required to yield data values. Typically this will be a class that provides a parser.

type CompatF a :: * -> * Source #

A type for wrapping migration results. It is most useful if this type
has `Alternative`

and `Monad`

instances, enabling the use of
`getCompatible`

. `Maybe`

is a good first choice.

getCompatible :: forall a. (Compat a, CompatConstraint a a, Alternative (CompatF a), Monad (CompatF a)) => (forall c. (Compat c, CompatConstraint a c) => CompatF a c) -> CompatF a a Source #

Recursively migrate a data value to the most recent schema, if possible.