Test.Feat.Modifiers

Types with invariants. Currently these are mostly examples of how to define such types, suggestions on useful types are appreciated.

To use the invariant types you can use the record label. For instance:

  data C a = C [a] [a] deriving Typeable
  instance Enumerable a => Enumerable (C a) where
     enumerate = unary $ funcurry $ 
       xs ys -> C (nonEmpty xs) (nonEmpty ys)

Alternatively you can put everything in pattern postition:

  instance Enumerable a => Enumerable (C a) where
     enumerate = unary $ funcurry $ 
       (Free (NonEmpty xs,NonEmpty ys)) -> C xs ys)

The first approach has the advantage of being usable with a point free style: xs -> C (nonEmpty xs) . nonEmpty .

Documentation

newtype NonEmpty a

A type of non empty lists.

Constructors

NonEmpty

Fields

nonEmpty :: [a]

Instances

Typeable1 NonEmpty

Show a => Show (NonEmpty a)

Enumerable a => Enumerable (NonEmpty a)

mkNonEmpty :: a -> [a] -> [a]

newtype Nat

A type of natural numbers.

Constructors

Nat

Fields

nat :: Integer

Instances

Show Nat

Typeable Nat

Enumerable Nat