testing-feat- Functional Enumeration of Algebraic Types

Safe HaskellNone




Everything you need to construct an enumeration for an algebraic type. Just define each constructor using pure for nullary constructors and unary and funcurry for positive arity constructors, then combine the constructors with consts. Example:

  instance Enumerable a => Enumerable [a] where
    enumerate = consts [unary (funcurry (:)), pure []]

There's also a handy Template Haskell function for automatic derivation.



class Typeable a => Enumerable a whereSource

A class of functionally enumerable types


enumerate :: Enumerate aSource

This is the interface for defining an instance. When combining enumerations use shared instead and when accessing the data of enumerations use optimal.

Building instances

nullary :: a -> Constructor aSource

For nullary constructors such as True and [].

unary :: Enumerable a => (a -> b) -> Constructor bSource

For any non-nullary constructor. Apply funcurry until the type of the result is unary (i.e. n-1 times where n is the number of fields of the constructor).

funcurry :: (a -> b -> c) -> FreePair a b -> cSource

Uncurry a function (typically a constructor) to a function on free pairs.

consts :: [Constructor a] -> Enumerate aSource

Produces the enumeration of a type given the enumerators for each of its constructors. The result of unary should typically not be used directly in an instance even if it only has one constructor. So you should apply consts even in that case.

Accessing the enumerator of an instance

shared :: Enumerable a => Enumerate aSource

Version of enumerate that ensures that the enumeration is shared between all accesses. Should always be used when combining enumerations.

optimal :: Enumerable a => Enumerate aSource

An optimal version of enumerate. Used by all library functions that access enumerated values (but not by combining functions). Library functions should ensure that optimal is not reevaluated.

Free pairs

newtype FreePair a b Source

A free pair constructor. The cost of constructing a free pair is equal to the sum of the costs of its components.




free :: (a, b)


Deriving instances with template Haskell

deriveEnumerable :: Name -> Q [Dec]Source

Derive an instance of Enumberable with Template Haskell. To derive an instance for Enumerable A, just put this as a top level declaration in your module (with the TemplateHaskell extension enabled):

   deriveEnumerable ''A

deriveEnumerable' :: ConstructorDeriv -> Q [Dec]Source

Derive an instance of Enumberable with Template Haskell, with rules for some specific constructors