Data.Comp.Param.Algebra

This module defines the notion of algebras and catamorphisms, and their generalizations to e.g. monadic versions and other (co)recursion schemes.

Algebras & Catamorphisms

type Alg f a = f a a -> a

This type represents an algebra over a difunctor f and carrier a.

free :: forall h f a b. Difunctor f => Alg f a -> (b -> a) -> Cxt h f a b -> a

Construct a catamorphism for contexts over f with holes of type b, from the given algebra.

cata :: forall f a. Difunctor f => Alg f a -> Term f -> a

Construct a catamorphism from the given algebra.

cata' :: Difunctor f => Alg f a -> Cxt h f a a -> a

A generalisation of cata from terms over f to contexts over f, where the holes have the type of the algebra carrier.

appCxt :: Difunctor f => Context f a (Cxt h f a b) -> Cxt h f a b

This function applies a whole context into another context.

Monadic Algebras & Catamorphisms

type AlgM m f a = f a a -> m a

This type represents a monadic algebra. It is similar to Alg but the return type is monadic.

algM :: (Ditraversable f, Monad m) => AlgM m f a -> Alg f (m a)

Convert a monadic algebra into an ordinary algebra with a monadic carrier.

freeM :: forall m h f a b. (Ditraversable f, Monad m) => AlgM m f a -> (b -> m a) -> Cxt h f a b -> m a

Construct a monadic catamorphism for contexts over f with holes of type b, from the given monadic algebra.

cataM :: forall m f a. (Ditraversable f, Monad m) => AlgM m f a -> Term f -> m a

Construct a monadic catamorphism from the given monadic algebra.

cataM' :: forall m h f a. (Ditraversable f, Monad m) => AlgM m f a -> Cxt h f a (m a) -> m a

A generalisation of cataM from terms over f to contexts over f, where the holes have the type of the monadic algebra carrier.

Term Homomorphisms

type CxtFun f g = forall h a b. Cxt h f a b -> Cxt h g a b

This type represents a context function.

type SigFun f g = forall a b. f a b -> g a b

This type represents a signature function.

type Hom f g = SigFun f (Context g)

This type represents a term homomorphism.

appHom :: forall f g. (Difunctor f, Difunctor g) => Hom f g -> CxtFun f g

Apply a term homomorphism recursively to a term/context.

appHom' :: forall f g. Difunctor g => Hom f g -> CxtFun f g

Apply a term homomorphism recursively to a term/context.

compHom :: (Difunctor g, Difunctor h) => Hom g h -> Hom f g -> Hom f h

Compose two term homomorphisms.

appSigFun :: forall f g. Difunctor f => SigFun f g -> CxtFun f g

This function applies a signature function to the given context.

appSigFun' :: forall f g. Difunctor g => SigFun f g -> CxtFun f g

This function applies a signature function to the given context. This is a top-bottom variant of appSigFun.

compSigFun :: SigFun g h -> SigFun f g -> SigFun f h

This function composes two signature functions.

compHomSigFun :: Hom g h -> SigFun f g -> Hom f h

This function composes a term homomorphism and a signature function.

compSigFunHom :: Difunctor g => SigFun g h -> Hom f g -> Hom f h

This function composes a term homomorphism and a signature function.

hom :: Difunctor g => SigFun f g -> Hom f g

Lifts the given signature function to the canonical term homomorphism.

compAlg :: (Difunctor f, Difunctor g) => Alg g a -> Hom f g -> Alg f a

Compose an algebra with a term homomorphism to get a new algebra.

compAlgSigFun :: Alg g a -> SigFun f g -> Alg f a

Monadic Term Homomorphisms

type CxtFunM m f g = forall h. SigFunM m (Cxt h f) (Cxt h g)

This type represents a monadic context function.

type SigFunM m f g = forall a b. f a b -> m (g a b)

This type represents a monadic signature function.

type HomM m f g = SigFunM m f (Context g)

This type represents a monadic term homomorphism.

type SigFunMD m f g = forall a b. f a (m b) -> m (g a b)

This type represents a monadic signature function. It is similar to SigFunM but has monadic values also in the domain.

type HomMD m f g = SigFunMD m f (Context g)

This type represents a monadic term homomorphism. It is similar to HomM but has monadic values also in the domain.

sigFunM :: Monad m => SigFun f g -> SigFunM m f g

Lift the given signature function to a monadic signature function. Note that term homomorphisms are instances of signature functions. Hence this function also applies to term homomorphisms.

appHomM :: forall f g m. (Ditraversable f, Difunctor g, Monad m) => HomM m f g -> CxtFunM m f g

Apply a monadic term homomorphism recursively to a term/context. The monad is sequenced bottom-up.

appTHomM :: (Ditraversable f, ParamFunctor m, Monad m, Difunctor g) => HomM m f g -> Term f -> m (Term g)

A restricted form of |appHomM| which only works for terms.

appHomM' :: forall f g m. (Ditraversable g, Monad m) => HomM m f g -> CxtFunM m f g

Apply a monadic term homomorphism recursively to a term/context. The monad is sequence top-down.

appTHomM' :: (Ditraversable g, ParamFunctor m, Monad m, Difunctor g) => HomM m f g -> Term f -> m (Term g)

A restricted form of |appHomM'| which only works for terms.

homM :: (Difunctor g, Monad m) => SigFunM m f g -> HomM m f g

Lift the given signature function to a monadic term homomorphism.

homMD :: forall f g m. (Difunctor f, Difunctor g, Monad m) => HomMD m f g -> CxtFunM m f g

This function constructs the unique monadic homomorphism from the initial term algebra to the given term algebra.

appSigFunM :: forall m f g. (Ditraversable f, Monad m) => SigFunM m f g -> CxtFunM m f g

This function applies a monadic signature function to the given context.

appTSigFunM :: (Ditraversable f, ParamFunctor m, Monad m, Difunctor g) => SigFunM m f g -> Term f -> m (Term g)

A restricted form of |appSigFunM| which only works for terms.

appSigFunM' :: forall m f g. (Ditraversable g, Monad m) => SigFunM m f g -> CxtFunM m f g

This function applies a monadic signature function to the given context. This is a 'top-down variant of appSigFunM.

appTSigFunM' :: (Ditraversable g, ParamFunctor m, Monad m, Difunctor g) => SigFunM m f g -> Term f -> m (Term g)

A restricted form of |appSigFunM'| which only works for terms.

appSigFunMD :: forall f g m. (Ditraversable f, Difunctor g, Monad m) => SigFunMD m f g -> CxtFunM m f g

This function applies a signature function to the given context.

appTSigFunMD :: (Ditraversable f, ParamFunctor m, Monad m, Difunctor g) => SigFunMD m f g -> Term f -> m (Term g)

A restricted form of |appSigFunMD| which only works for terms.

compHomM :: (Ditraversable g, Difunctor h, Monad m) => HomM m g h -> HomM m f g -> HomM m f h

Compose two monadic term homomorphisms.

compHomM' :: (Ditraversable h, Monad m) => HomM m g h -> HomM m f g -> HomM m f h

Compose two monadic term homomorphisms.

compSigFunM :: Monad m => SigFunM m g h -> SigFunM m f g -> SigFunM m f h

This function composes two monadic signature functions.

compSigFunHomM :: (Ditraversable g, Monad m) => SigFunM m g h -> HomM m f g -> HomM m f h

Compose two monadic term homomorphisms.

compSigFunHomM' :: (Ditraversable h, Monad m) => SigFunM m g h -> HomM m f g -> HomM m f h

Compose two monadic term homomorphisms.

compAlgSigFunM :: Monad m => AlgM m g a -> SigFunM m f g -> AlgM m f a

Compose a monadic algebra with a monadic signature function to get a new monadic algebra.

compAlgSigFunM' :: AlgM m g a -> SigFun f g -> AlgM m f a

Compose a monadic algebra with a signature function to get a new monadic algebra.

compAlgM :: (Ditraversable g, Monad m) => AlgM m g a -> HomM m f g -> AlgM m f a

Compose a monadic algebra with a monadic term homomorphism to get a new monadic algebra.

compAlgM' :: (Ditraversable g, Monad m) => AlgM m g a -> Hom f g -> AlgM m f a

Compose a monadic algebra with a term homomorphism to get a new monadic algebra.

Coalgebras & Anamorphisms

type Coalg f a = forall b. a -> [(a, b)] -> Either b (f b (a, [(a, b)]))

This type represents a coalgebra over a difunctor f and carrier a. The list of (a,b)s represent the parameters that may occur in the constructed value. The first component represents the seed of the parameter, and the second component is the (polymorphic) parameter itself. If f is itself a binder, then the parameters bound by f can be passed to the covariant argument, thereby making them available to sub terms.

ana :: Difunctor f => Coalg f a -> a -> Term f

Construct an anamorphism from the given coalgebra.

type CoalgM m f a = forall b. a -> [(a, b)] -> m (Either b (f b (a, [(a, b)])))

This type represents a monadic coalgebra over a difunctor f and carrier a.

anaM :: forall a m f. (Ditraversable f, Monad m) => CoalgM m f a -> a -> forall a. m (Trm f a)

Construct a monadic anamorphism from the given monadic coalgebra.

R-Algebras & Paramorphisms

type RAlg f a = f a (Trm f a, a) -> a

This type represents an r-algebra over a difunctor f and carrier a.

para :: forall f a. Difunctor f => RAlg f a -> Term f -> a

Construct a paramorphism from the given r-algebra.

type RAlgM m f a = f a (Trm f a, a) -> m a

This type represents a monadic r-algebra over a difunctor f and carrier a.

paraM :: forall m f a. (Ditraversable f, Monad m) => RAlgM m f a -> Term f -> m a

Construct a monadic paramorphism from the given monadic r-algebra.

R-Coalgebras & Apomorphisms

type RCoalg f a = forall b. a -> [(a, b)] -> Either b (f b (Either (Trm f b) (a, [(a, b)])))

This type represents an r-coalgebra over a difunctor f and carrier a.

apo :: Difunctor f => RCoalg f a -> a -> Term f

Construct an apomorphism from the given r-coalgebra.

type RCoalgM m f a = forall b. a -> [(a, b)] -> m (Either b (f b (Either (Trm f b) (a, [(a, b)]))))

This type represents a monadic r-coalgebra over a functor f and carrier a.

apoM :: forall f m a. (Ditraversable f, Monad m) => RCoalgM m f a -> a -> forall a. m (Trm f a)

Construct a monadic apomorphism from the given monadic r-coalgebra.

CV-Algebras & Histomorphisms

type CVAlg f a f' = f a (Trm f' a) -> a

This type represents a cv-algebra over a difunctor f and carrier a.

histo :: forall f f' a. (Difunctor f, DistAnn f a f') => CVAlg f a f' -> Term f -> a

Construct a histomorphism from the given cv-algebra.

type CVAlgM m f a f' = f a (Trm f' a) -> m a

This type represents a monadic cv-algebra over a functor f and carrier a.

histoM :: forall f f' m a. (Ditraversable f, Monad m, DistAnn f a f') => CVAlgM m f a f' -> Term f -> m a

Construct a monadic histomorphism from the given monadic cv-algebra.

CV-Coalgebras & Futumorphisms

type CVCoalg f a = forall b. a -> [(a, b)] -> Either b (f b (Context f b (a, [(a, b)])))

This type represents a cv-coalgebra over a difunctor f and carrier a. The list of (a,b)s represent the parameters that may occur in the constructed value. The first component represents the seed of the parameter, and the second component is the (polymorphic) parameter itself. If f is itself a binder, then the parameters bound by f can be passed to the covariant argument, thereby making them available to sub terms.

futu :: Difunctor f => CVCoalg f a -> a -> Term f

Construct a futumorphism from the given cv-coalgebra.

type CVCoalg' f a = forall b. a -> [(a, b)] -> Context f b (a, [(a, b)])

This type represents a generalised cv-coalgebra over a difunctor f and carrier a.

futu' :: Difunctor f => CVCoalg' f a -> a -> Term f

Construct a futumorphism from the given generalised cv-coalgebra.

type CVCoalgM m f a = forall b. a -> [(a, b)] -> m (Either b (f b (Context f b (a, [(a, b)]))))

This type represents a monadic cv-coalgebra over a difunctor f and carrier a.

futuM :: forall f a m. (Ditraversable f, Monad m) => CVCoalgM m f a -> a -> forall a. m (Trm f a)

Construct a monadic futumorphism from the given monadic cv-coalgebra.