Data.Vinyl.CoRec

Co-records: open sum types.

Consider a record with three fields A, B, and C. A record is a product of its fields; that is, it contains all of them: A, B, and C. If we want to talk about a value whose type is one of those three types, it is any one of type A, B, or C. The type CoRec '[A,B,C] corresponds to this sum type.

Documentation

data CoRec :: (k -> *) -> [k] -> * where

Generalize algebraic sum types.

Constructors

CoRec :: RElem a ts (RIndex a ts) => !(f a) -> CoRec f ts

Instances

(RecApplicative ts, RecordToList ts, RZipWith ts, ReifyConstraint Eq Maybe ts, RMap ts) => Eq (CoRec Identity ts)

Defined in Data.Vinyl.CoRec

Methods

(==) :: CoRec Identity ts -> CoRec Identity ts -> Bool

(/=) :: CoRec Identity ts -> CoRec Identity ts -> Bool

(RPureConstrained Show ts, RecApplicative ts) => Show (CoRec Identity ts)

Defined in Data.Vinyl.CoRec

Methods

showsPrec :: Int -> CoRec Identity ts -> ShowS

show :: CoRec Identity ts -> String

showList :: [CoRec Identity ts] -> ShowS

foldCoRec :: (forall a. RElem a ts (RIndex a ts) => f a -> b) -> CoRec f ts -> b

Apply a function to a CoRec value. The function must accept any variant.

type Field = CoRec Identity

A Field of a Rec Identity is a CoRec Identity.

newtype Op b a

A function type constructor that takes its arguments in the reverse order.

Constructors

Op

Fields

• runOp :: a -> b

coRecToRec :: forall f ts. RecApplicative ts => CoRec f ts -> Rec (Maybe :. f) ts

We can inject a a CoRec into a Rec where every field of the Rec is Nothing except for the one whose type corresponds to the type of the given CoRec variant.

coRecToRec' :: (RecApplicative ts, RMap ts) => CoRec Identity ts -> Rec Maybe ts

Shorthand for applying coRecToRec with common functors.

class FoldRec ss ts where

Fold a field selection function over a Rec.

Minimal complete definition

foldRec

Methods

foldRec :: (CoRec f ss -> CoRec f ss -> CoRec f ss) -> CoRec f ss -> Rec f ts -> CoRec f ss

Instances

FoldRec (ss :: [k]) ([] :: [k])

Defined in Data.Vinyl.CoRec

Methods

foldRec :: (CoRec f ss -> CoRec f ss -> CoRec f ss) -> CoRec f ss -> Rec f [] -> CoRec f ss

(t ∈ ss, FoldRec ss ts) => FoldRec (ss :: [a]) (t ': ts :: [a])

Defined in Data.Vinyl.CoRec

Methods

foldRec :: (CoRec f ss -> CoRec f ss -> CoRec f ss) -> CoRec f ss -> Rec f (t ': ts) -> CoRec f ss

coRecMap :: (forall x. f x -> g x) -> CoRec f ts -> CoRec g ts

Apply a natural transformation to a variant.

data DictOnly c a where

Capture a type class instance dictionary

Constructors

DictOnly :: c a => DictOnly c a

getDict :: forall c ts a proxy. (a ∈ ts, RPureConstrained c ts) => proxy a -> DictOnly c a

Get a DictOnly from an RPureConstrained instance.

coRecMapC :: forall c ts f g. RPureConstrained c ts => (forall x. (x ∈ ts, c x) => f x -> g x) -> CoRec f ts -> CoRec g ts

Like coRecMap, but the function mapped over the CoRec can have a constraint.

coRecTraverse :: Functor h => (forall x. f x -> h (g x)) -> CoRec f ts -> h (CoRec g ts)

This can be used to pull effects out of a CoRec.

foldRec1 :: FoldRec (t ': ts) ts => (CoRec f (t ': ts) -> CoRec f (t ': ts) -> CoRec f (t ': ts)) -> Rec f (t ': ts) -> CoRec f (t ': ts)

Fold a field selection function over a non-empty Rec.

firstField :: FoldRec ts ts => Rec (Maybe :. f) ts -> Maybe (CoRec f ts)

Similar to First: find the first field that is not Nothing.

lastField :: FoldRec ts ts => Rec (Maybe :. f) ts -> Maybe (CoRec f ts)

Similar to Last: find the last field that is not Nothing.

onCoRec :: forall c f ts b g. RPureConstrained c ts => (forall a. (a ∈ ts, c a) => f a -> g b) -> CoRec f ts -> g b

Apply methods from a type class to a CoRec. Intended for use with TypeApplications, e.g. onCoRec @Show show r

onField :: forall c ts b. RPureConstrained c ts => (forall a. (a ∈ ts, c a) => a -> b) -> Field ts -> b

Apply a type class method to a Field. Intended for use with TypeApplications, e.g. onField @Show show r.

Extracting values from a CoRec/Pattern matching on a CoRec

variantIndexOf :: forall f ts. CoRec f ts -> Int

Compute a runtime Int index identifying the position of the variant held by a CoRec f ts in the type-level list ts.

asA :: NatToInt (RIndex t ts) => CoRec Identity ts -> Maybe t

If a CoRec is a variant of the requested type, return Just that value; otherwise return Nothing.

asA' :: forall t ts f. NatToInt (RIndex t ts) => CoRec f ts -> Maybe (f t)

Like asA, but for any interpretation functor.

match :: forall ts b. CoRec Identity ts -> Handlers ts b -> b

Pattern match on a CoRec by specifying handlers for each case. Note that the order of the Handlers has to match the type level list (t:ts).

>>> :{
let testCoRec = Col (Identity False) :: CoRec Identity [Int, String, Bool] in
match testCoRec $
      (H $ \i -> "my Int is the successor of " ++ show (i - 1))
   :& (H $ \s -> "my String is: " ++ s)
   :& (H $ \b -> "my Bool is not: " ++ show (not b) ++ " thus it is " ++ show b)
   :& RNil
:}
"my Bool is not: True thus it is False"

class RIndex t ts ~ i => Match1 t ts i where

Helper for handling a variant of a CoRec: either the function is applied to the variant or the type of the CoRec is refined to reflect the fact that the variant is not compatible with the type of the would-be handler.

Minimal complete definition

match1'

Methods

match1' :: Handler r t -> Rec Maybe ts -> Either r (Rec Maybe (RDelete t ts))

Instances

Match1 t (t ': ts) Z

Defined in Data.Vinyl.CoRec

Methods

match1' :: Handler r t -> Rec Maybe (t ': ts) -> Either r (Rec Maybe (RDelete t (t ': ts)))

(Match1 t ts i, RIndex t (s ': ts) ~ S i, RDelete t (s ': ts) ~ (s ': RDelete t ts)) => Match1 t (s ': ts) (S i)

Defined in Data.Vinyl.CoRec

Methods

match1' :: Handler r t -> Rec Maybe (s ': ts) -> Either r (Rec Maybe (RDelete t (s ': ts)))

match1 :: (Match1 t ts (RIndex t ts), RecApplicative ts, RMap ts, RMap (RDelete t ts), FoldRec (RDelete t ts) (RDelete t ts)) => Handler r t -> CoRec Identity ts -> Either r (CoRec Identity (RDelete t ts))

Handle a single variant of a CoRec: either the function is applied to the variant or the type of the CoRec is refined to reflect the fact that the variant is not compatible with the type of the would-be handler

matchNil :: CoRec f '[] -> r

newtype Handler b a

Newtype around functions for a to b

Constructors

H (a -> b)

type Handlers ts b = Rec (Handler b) ts

'Handlers ts b', is essentially a list of functions, one for each type in ts. All functions produce a value of type b. Hence, 'Handlers ts b' would represent something like the type-level list: [t -> b | t in ts ]

restrictCoRec :: forall t ts f. (RecApplicative ts, FoldRec ts ts) => CoRec f (t ': ts) -> Either (f t) (CoRec f ts)

A CoRec is either the first possible variant indicated by its type, or a CoRec that must be one of the remaining types.

weakenCoRec :: (RecApplicative ts, FoldRec (t ': ts) (t ': ts)) => CoRec f ts -> CoRec f (t ': ts)

A CoRec whose possible types are ts may be used at a type of CoRec whose possible types are t:ts.

Safe Variants

restrictCoRecSafe :: forall t ts f. (RecApplicative ts, FoldRec ts ts) => CoRec f (t ': ts) -> Either (f t) (CoRec f ts)

A CoRec is either the first possible variant indicated by its type, or a CoRec that must be one of the remaining types. The safety is related to that of asASafe.

asASafe :: (t ∈ ts, RecApplicative ts, RMap ts) => CoRec Identity ts -> Maybe t

Like asA, but implemented more safely and typically slower.

asA'Safe :: (t ∈ ts, RecApplicative ts, RMap ts) => CoRec f ts -> (Maybe :. f) t

Like asASafe, but for any interpretation functor.