Safe Haskell | Safe |
---|---|

Language | Haskell2010 |

This module contains an extensible error infrastructure.

Each kind of errors gets a separate type class which encodes
a `Prism`

(roughly a getter and a constructor). The `Reader`

s, then,
have the constraints for precisely the set of errors they can return.

# Documentation

The type of errors returned by `envparse`

's `Reader`

s. These fall into 3
categories:

- Variables that are unset in the environment.
- Variables whose value is empty.
- Variables whose value cannot be parsed using the
`Read`

instance.

The class of types that contain and can be constructed from the error returned from parsing unset variables.

The class of types that contain and can be constructed from the error returned from parsing variables whose value is empty.