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

(RecAll * Maybe ts Eq, RecApplicative * ts) => Eq (CoRec * Identity ts)

Methods

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

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

(AllConstrained * Show ts, RecApplicative * ts) => Show (CoRec * Identity ts)

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 :: 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 => 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 k ss ([] k)

Methods

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

((∈) a t ss, FoldRec a ss ts) => FoldRec a ss ((:) a t ts)

Methods

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

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

Apply a natural transformation to a variant.

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 cs f ts b. (AllAllSat cs ts, Functor f, RecApplicative ts) => Proxy cs -> (forall a. AllSatisfied cs a => a -> b) -> CoRec f ts -> f b

Apply a type class method on a CoRec. The first argument is a Proxy value for a list of Constraint constructors. For example, onCoRec [pr|Num,Ord|] (> 20) r. If only one constraint is needed, use the pr1 quasiquoter.

onField :: forall cs ts b. (AllAllSat cs ts, RecApplicative ts) => Proxy cs -> (forall a. AllSatisfied cs a => a -> b) -> Field ts -> b

Apply a type class method on a Field. The first argument is a Proxy value for a list of Constraint constructors. For example, onCoRec [pr|Num,Ord|] (> 20) r. If only one constraint is needed, use the pr1 quasiquoter.

reifyDicts :: forall cs f proxy ts. (AllAllSat cs ts, RecApplicative ts) => proxy cs -> (forall a. AllSatisfied cs a => f a) -> Rec f ts

Build a record whose elements are derived solely from a list of constraint constructors satisfied by each.

Extracting values from a CoRec/Pattern matching on a CoRec

asA :: (t ∈ ts, RecApplicative ts) => proxy t -> CoRec Identity ts -> Maybe t

Given a proxy of type t and a 'CoRec Identity' that might be a t, try to convert the CoRec to a t.

match :: RecApplicative (t ': ts) => CoRec Identity (t ': ts) -> Handlers (t ': ts) b -> b

Pattern match on a CoRec by specifying handlers for each case. If the CoRec is non-empty this function is total. 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"

match' :: RecApplicative ts => CoRec Identity ts -> Handlers ts b -> Maybe b

Pattern match on a CoRec by specifying handlers for each case. The only case in which this can produce a Nothing is if the list ts is empty.

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

Methods

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

(Match1 t ts i, (~) Nat (RIndex * t ((:) * s ts)) (S i), (~) [*] (RDelete * t ((:) * s ts)) ((:) * s (RDelete * t ts))) => Match1 t ((:) * s ts) (S i)

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, 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 ]