Annotations.MultiRec.ErrorAlg

Documentation

type family ErrorAlg f e a :: *

Type family that converts pattern functors to convenient algebra types.

Instances

type ErrorAlg U e a = Either e a

type ErrorAlg ((:+:) f g) e a = (ErrorAlg f e a, ErrorAlg g e a)

type ErrorAlg ((:*:) (I xi) f) e a = a -> ErrorAlg f e a

type ErrorAlg ((:*:) (K b) f) e a = b -> ErrorAlg f e a

type ErrorAlg ((:>:) f xi) e a = ErrorAlg f e a

type ErrorAlg_PF f e a = forall ix. f (K0 a) ix -> Either e a

An error algebra over pattern functors.

class MkErrorAlg f where

Converts convenient algebras to algebras that are able to work with pattern functors.

Methods

mkErrorAlg :: ErrorAlg f e a -> ErrorAlg_PF f e a

Instances

MkErrorAlg U

(MkErrorAlg f, MkErrorAlg g) => MkErrorAlg ((:+:) f g)

MkErrorAlg f => MkErrorAlg ((:*:) (I xi) f)

MkErrorAlg f => MkErrorAlg ((:*:) (K a) f)

MkErrorAlg f => MkErrorAlg ((:>:) f xi)

errorCata :: HFunctor phi f => ErrorAlg_PF f e r -> phi ix -> HFix (K x :*: f) ix -> Except [(e, x)] r

Reduces a tree to a value according to the algebra, collecting potential errors. The errors are combined with the annotations in the tree at the positions at which the errors occurred.

(&) :: a -> b -> (a, b) infixr 5

For constructing algebras that are made of nested pairs rather than n-ary tuples, it is helpful to use this pairing combinator.