# QuickCheckVariant

Generator of "valid" and "invalid" data in a type class

For example, if you created

```haskell
data Person = Anonymous { getId::String } | Client { getUsername::String, getName::String, getEmail::String} deriving(Show,Eq)
```

We can provide means to generate valid and invalid data, like:

```haskell
instance Variant Person where
  valid = do
    id <- alternative
    username <- alternative
    name <- alternative
    domain <- alternative
    ext <- alternative
    (oneof . return) [Anonymous id, Client username name (username++"@"++domain++ext)]
  invalid = do
    username <- alternative
    name <- alternative
    return $ Client username name ""

``` 

See [this post](https://wiki.haskell.org/QuickCheck_as_a_test_set_generator) for more details