Data.PartialSemigroup.Generics

If a type derives Generic and all of its fields have PartialSemigroup instances, you can get a PartialSemigroup for free using genericPartialSemigroupOp.

Example

For this demonstration we'll define a contrived example type T with two constructors, A and B.

>>> data T = A String (Either String String) | B String deriving (Generic, Show)

And then define its PartialSemigroup instance using genericPartialSemigroupOp.

>>> instance PartialSemigroup T where (<>?) = genericPartialSemigroupOp

This gives us an implementation of <>? which combines values only if they have the same structure.

>>> A "s" (Left "x") <>? A "t" (Left "y")
Just (A "st" (Left "xy"))

>>> B "x" <>? B "y"
Just (B "xy")

For values that do not have the same structure, <>? produces Nothing.

>>> A "s" (Left "x") <>? A "t" (Right "y")
Nothing

>>> A "x" (Left "y") <>? B "z"
Nothing

The generic PartialSemigroup operator

genericPartialSemigroupOp :: (Generic a, PartialSemigroupRep (Rep a)) => a -> a -> Maybe a

Implementation details

class PartialSemigroupRep rep where

The class of generic type Reps for which we can automatically derive PartialSemigroup:

• K1 - a single value
• M1 - a value with some additional metadata (which we simply discard)
• :+: - sum types
• :*: - product types

Methods

repPartialSemigroupOp :: rep a -> rep a -> Maybe (rep a)

Instances

(PartialSemigroupRep rep1, PartialSemigroupRep rep2) => PartialSemigroupRep (rep1 :*: rep2 :: k -> Type)

Defined in Data.PartialSemigroup.Generics

Methods

repPartialSemigroupOp :: forall (a :: k0). (rep1 :*: rep2) a -> (rep1 :*: rep2) a -> Maybe ((rep1 :*: rep2) a)

(PartialSemigroupRep rep1, PartialSemigroupRep rep2) => PartialSemigroupRep (rep1 :+: rep2 :: k -> Type)

Defined in Data.PartialSemigroup.Generics

Methods

repPartialSemigroupOp :: forall (a :: k0). (rep1 :+: rep2) a -> (rep1 :+: rep2) a -> Maybe ((rep1 :+: rep2) a)

PartialSemigroup a => PartialSemigroupRep (K1 i a :: k -> Type)

Defined in Data.PartialSemigroup.Generics

Methods

repPartialSemigroupOp :: forall (a0 :: k0). K1 i a a0 -> K1 i a a0 -> Maybe (K1 i a a0)

PartialSemigroupRep rep => PartialSemigroupRep (M1 i meta rep :: k -> Type)

Defined in Data.PartialSemigroup.Generics

Methods

repPartialSemigroupOp :: forall (a :: k0). M1 i meta rep a -> M1 i meta rep a -> Maybe (M1 i meta rep a)

Re-exports

class Generic a

Representable types of kind *. This class is derivable in GHC with the DeriveGeneric flag on.

A Generic instance must satisfy the following laws:

from . to ≡ id
to . from ≡ id

Minimal complete definition

from, to

Instances

Generic All

Defined in Data.Semigroup.Internal

Associated Types

type Rep All :: Type -> Type

Methods

from :: All -> Rep All x

to :: Rep All x -> All

Generic Any

Defined in Data.Semigroup.Internal

Associated Types

type Rep Any :: Type -> Type

Methods

from :: Any -> Rep Any x

to :: Rep Any x -> Any

Generic Fingerprint

Defined in GHC.Generics

Associated Types

type Rep Fingerprint :: Type -> Type

Methods

from :: Fingerprint -> Rep Fingerprint x

to :: Rep Fingerprint x -> Fingerprint

Generic Associativity

Defined in GHC.Generics

Associated Types

type Rep Associativity :: Type -> Type

Methods

from :: Associativity -> Rep Associativity x

to :: Rep Associativity x -> Associativity

Generic DecidedStrictness

Defined in GHC.Generics

Associated Types

type Rep DecidedStrictness :: Type -> Type

Methods

from :: DecidedStrictness -> Rep DecidedStrictness x

to :: Rep DecidedStrictness x -> DecidedStrictness

Generic Fixity

Defined in GHC.Generics

Associated Types

type Rep Fixity :: Type -> Type

Methods

from :: Fixity -> Rep Fixity x

to :: Rep Fixity x -> Fixity

Generic SourceStrictness

Defined in GHC.Generics

Associated Types

type Rep SourceStrictness :: Type -> Type

Methods

from :: SourceStrictness -> Rep SourceStrictness x

to :: Rep SourceStrictness x -> SourceStrictness

Generic SourceUnpackedness

Defined in GHC.Generics

Associated Types

type Rep SourceUnpackedness :: Type -> Type

Methods

from :: SourceUnpackedness -> Rep SourceUnpackedness x

to :: Rep SourceUnpackedness x -> SourceUnpackedness

Generic SrcLoc

Defined in GHC.Generics

Associated Types

type Rep SrcLoc :: Type -> Type

Methods

from :: SrcLoc -> Rep SrcLoc x

to :: Rep SrcLoc x -> SrcLoc

Generic GeneralCategory

Defined in GHC.Generics

Associated Types

type Rep GeneralCategory :: Type -> Type

Methods

from :: GeneralCategory -> Rep GeneralCategory x

to :: Rep GeneralCategory x -> GeneralCategory

Generic Ordering

Defined in GHC.Generics

Associated Types

type Rep Ordering :: Type -> Type

Methods

from :: Ordering -> Rep Ordering x

to :: Rep Ordering x -> Ordering

Generic ()

Defined in GHC.Generics

Associated Types

type Rep () :: Type -> Type

Methods

from :: () -> Rep () x

to :: Rep () x -> ()

Generic Bool

Defined in GHC.Generics

Associated Types

type Rep Bool :: Type -> Type

Methods

from :: Bool -> Rep Bool x

to :: Rep Bool x -> Bool

Generic (ZipList a)

Defined in Control.Applicative

Associated Types

type Rep (ZipList a) :: Type -> Type

Methods

from :: ZipList a -> Rep (ZipList a) x

to :: Rep (ZipList a) x -> ZipList a

Generic (Identity a)

Defined in Data.Functor.Identity

Associated Types

type Rep (Identity a) :: Type -> Type

Methods

from :: Identity a -> Rep (Identity a) x

to :: Rep (Identity a) x -> Identity a

Generic (First a)

Defined in Data.Monoid

Associated Types

type Rep (First a) :: Type -> Type

Methods

from :: First a -> Rep (First a) x

to :: Rep (First a) x -> First a

Generic (Last a)

Defined in Data.Monoid

Associated Types

type Rep (Last a) :: Type -> Type

Methods

from :: Last a -> Rep (Last a) x

to :: Rep (Last a) x -> Last a

Generic (Down a)

Defined in GHC.Generics

Associated Types

type Rep (Down a) :: Type -> Type

Methods

from :: Down a -> Rep (Down a) x

to :: Rep (Down a) x -> Down a

Generic (First a)

Defined in Data.Semigroup

Associated Types

type Rep (First a) :: Type -> Type

Methods

from :: First a -> Rep (First a) x

to :: Rep (First a) x -> First a

Generic (Last a)

Defined in Data.Semigroup

Associated Types

type Rep (Last a) :: Type -> Type

Methods

from :: Last a -> Rep (Last a) x

to :: Rep (Last a) x -> Last a

Generic (Max a)

Defined in Data.Semigroup

Associated Types

type Rep (Max a) :: Type -> Type

Methods

from :: Max a -> Rep (Max a) x

to :: Rep (Max a) x -> Max a

Generic (Min a)

Defined in Data.Semigroup

Associated Types

type Rep (Min a) :: Type -> Type

Methods

from :: Min a -> Rep (Min a) x

to :: Rep (Min a) x -> Min a

Generic (WrappedMonoid m)

Defined in Data.Semigroup

Associated Types

type Rep (WrappedMonoid m) :: Type -> Type

Methods

from :: WrappedMonoid m -> Rep (WrappedMonoid m) x

to :: Rep (WrappedMonoid m) x -> WrappedMonoid m

Generic (Dual a)

Defined in Data.Semigroup.Internal

Associated Types

type Rep (Dual a) :: Type -> Type

Methods

from :: Dual a -> Rep (Dual a) x

to :: Rep (Dual a) x -> Dual a

Generic (Endo a)

Defined in Data.Semigroup.Internal

Associated Types

type Rep (Endo a) :: Type -> Type

Methods

from :: Endo a -> Rep (Endo a) x

to :: Rep (Endo a) x -> Endo a

Generic (Product a)

Defined in Data.Semigroup.Internal

Associated Types

type Rep (Product a) :: Type -> Type

Methods

from :: Product a -> Rep (Product a) x

to :: Rep (Product a) x -> Product a

Generic (Sum a)

Defined in Data.Semigroup.Internal

Associated Types

type Rep (Sum a) :: Type -> Type

Methods

from :: Sum a -> Rep (Sum a) x

to :: Rep (Sum a) x -> Sum a

Generic (Par1 p)

Defined in GHC.Generics

Associated Types

type Rep (Par1 p) :: Type -> Type

Methods

from :: Par1 p -> Rep (Par1 p) x

to :: Rep (Par1 p) x -> Par1 p

Generic (NonEmpty a)

Defined in GHC.Generics

Associated Types

type Rep (NonEmpty a) :: Type -> Type

Methods

from :: NonEmpty a -> Rep (NonEmpty a) x

to :: Rep (NonEmpty a) x -> NonEmpty a

Generic (Maybe a)

Defined in GHC.Generics

Associated Types

type Rep (Maybe a) :: Type -> Type

Methods

from :: Maybe a -> Rep (Maybe a) x

to :: Rep (Maybe a) x -> Maybe a

Generic (a)

Defined in GHC.Generics

Associated Types

type Rep (a) :: Type -> Type

Methods

from :: (a) -> Rep (a) x

to :: Rep (a) x -> (a)

Generic [a]

Defined in GHC.Generics

Associated Types

type Rep [a] :: Type -> Type

Methods

from :: [a] -> Rep [a] x

to :: Rep [a] x -> [a]

Generic (WrappedMonad m a)

Defined in Control.Applicative

Associated Types

type Rep (WrappedMonad m a) :: Type -> Type

Methods

from :: WrappedMonad m a -> Rep (WrappedMonad m a) x

to :: Rep (WrappedMonad m a) x -> WrappedMonad m a

Generic (Either a b)

Defined in GHC.Generics

Associated Types

type Rep (Either a b) :: Type -> Type

Methods

from :: Either a b -> Rep (Either a b) x

to :: Rep (Either a b) x -> Either a b

Generic (Proxy t)

Defined in GHC.Generics

Associated Types

type Rep (Proxy t) :: Type -> Type

Methods

from :: Proxy t -> Rep (Proxy t) x

to :: Rep (Proxy t) x -> Proxy t

Generic (Arg a b)

Defined in Data.Semigroup

Associated Types

type Rep (Arg a b) :: Type -> Type

Methods

from :: Arg a b -> Rep (Arg a b) x

to :: Rep (Arg a b) x -> Arg a b

Generic (U1 p)

Defined in GHC.Generics

Associated Types

type Rep (U1 p) :: Type -> Type

Methods

from :: U1 p -> Rep (U1 p) x

to :: Rep (U1 p) x -> U1 p

Generic (V1 p)

Defined in GHC.Generics

Associated Types

type Rep (V1 p) :: Type -> Type

Methods

from :: V1 p -> Rep (V1 p) x

to :: Rep (V1 p) x -> V1 p

Generic (a, b)

Defined in GHC.Generics

Associated Types

type Rep (a, b) :: Type -> Type

Methods

from :: (a, b) -> Rep (a, b) x

to :: Rep (a, b) x -> (a, b)

Generic (WrappedArrow a b c)

Defined in Control.Applicative

Associated Types

type Rep (WrappedArrow a b c) :: Type -> Type

Methods

from :: WrappedArrow a b c -> Rep (WrappedArrow a b c) x

to :: Rep (WrappedArrow a b c) x -> WrappedArrow a b c

Generic (Ap f a)

Defined in Data.Monoid

Associated Types

type Rep (Ap f a) :: Type -> Type

Methods

from :: Ap f a -> Rep (Ap f a) x

to :: Rep (Ap f a) x -> Ap f a

Generic (Alt f a)

Defined in Data.Semigroup.Internal

Associated Types

type Rep (Alt f a) :: Type -> Type

Methods

from :: Alt f a -> Rep (Alt f a) x

to :: Rep (Alt f a) x -> Alt f a

Generic (Rec1 f p)

Defined in GHC.Generics

Associated Types

type Rep (Rec1 f p) :: Type -> Type

Methods

from :: Rec1 f p -> Rep (Rec1 f p) x

to :: Rep (Rec1 f p) x -> Rec1 f p

Generic (URec (Ptr ()) p)

Defined in GHC.Generics

Associated Types

type Rep (URec (Ptr ()) p) :: Type -> Type

Methods

from :: URec (Ptr ()) p -> Rep (URec (Ptr ()) p) x

to :: Rep (URec (Ptr ()) p) x -> URec (Ptr ()) p

Generic (URec Char p)

Defined in GHC.Generics

Associated Types

type Rep (URec Char p) :: Type -> Type

Methods

from :: URec Char p -> Rep (URec Char p) x

to :: Rep (URec Char p) x -> URec Char p

Generic (URec Double p)

Defined in GHC.Generics

Associated Types

type Rep (URec Double p) :: Type -> Type

Methods

from :: URec Double p -> Rep (URec Double p) x

to :: Rep (URec Double p) x -> URec Double p

Generic (URec Float p)

Defined in GHC.Generics

Associated Types

type Rep (URec Float p) :: Type -> Type

Methods

from :: URec Float p -> Rep (URec Float p) x

to :: Rep (URec Float p) x -> URec Float p

Generic (URec Int p)

Defined in GHC.Generics

Associated Types

type Rep (URec Int p) :: Type -> Type

Methods

from :: URec Int p -> Rep (URec Int p) x

to :: Rep (URec Int p) x -> URec Int p

Generic (URec Word p)

Defined in GHC.Generics

Associated Types

type Rep (URec Word p) :: Type -> Type

Methods

from :: URec Word p -> Rep (URec Word p) x

to :: Rep (URec Word p) x -> URec Word p

Generic (a, b, c)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c) :: Type -> Type

Methods

from :: (a, b, c) -> Rep (a, b, c) x

to :: Rep (a, b, c) x -> (a, b, c)

Generic ((f :*: g) p)

Defined in GHC.Generics

Associated Types

type Rep ((f :*: g) p) :: Type -> Type

Methods

from :: (f :*: g) p -> Rep ((f :*: g) p) x

to :: Rep ((f :*: g) p) x -> (f :*: g) p

Generic ((f :+: g) p)

Defined in GHC.Generics

Associated Types

type Rep ((f :+: g) p) :: Type -> Type

Methods

from :: (f :+: g) p -> Rep ((f :+: g) p) x

to :: Rep ((f :+: g) p) x -> (f :+: g) p

Generic (K1 i c p)

Defined in GHC.Generics

Associated Types

type Rep (K1 i c p) :: Type -> Type

Methods

from :: K1 i c p -> Rep (K1 i c p) x

to :: Rep (K1 i c p) x -> K1 i c p

Generic (a, b, c, d)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d) :: Type -> Type

Methods

from :: (a, b, c, d) -> Rep (a, b, c, d) x

to :: Rep (a, b, c, d) x -> (a, b, c, d)

Generic ((f :.: g) p)

Defined in GHC.Generics

Associated Types

type Rep ((f :.: g) p) :: Type -> Type

Methods

from :: (f :.: g) p -> Rep ((f :.: g) p) x

to :: Rep ((f :.: g) p) x -> (f :.: g) p

Generic (M1 i c f p)

Defined in GHC.Generics

Associated Types

type Rep (M1 i c f p) :: Type -> Type

Methods

from :: M1 i c f p -> Rep (M1 i c f p) x

to :: Rep (M1 i c f p) x -> M1 i c f p

Generic (a, b, c, d, e)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e) :: Type -> Type

Methods

from :: (a, b, c, d, e) -> Rep (a, b, c, d, e) x

to :: Rep (a, b, c, d, e) x -> (a, b, c, d, e)

Generic (a, b, c, d, e, f)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f) :: Type -> Type

Methods

from :: (a, b, c, d, e, f) -> Rep (a, b, c, d, e, f) x

to :: Rep (a, b, c, d, e, f) x -> (a, b, c, d, e, f)

Generic (a, b, c, d, e, f, g)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g) -> Rep (a, b, c, d, e, f, g) x

to :: Rep (a, b, c, d, e, f, g) x -> (a, b, c, d, e, f, g)

Generic (a, b, c, d, e, f, g, h)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h) -> Rep (a, b, c, d, e, f, g, h) x

to :: Rep (a, b, c, d, e, f, g, h) x -> (a, b, c, d, e, f, g, h)

Generic (a, b, c, d, e, f, g, h, i)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i) -> Rep (a, b, c, d, e, f, g, h, i) x

to :: Rep (a, b, c, d, e, f, g, h, i) x -> (a, b, c, d, e, f, g, h, i)

Generic (a, b, c, d, e, f, g, h, i, j)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i, j) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i, j) -> Rep (a, b, c, d, e, f, g, h, i, j) x

to :: Rep (a, b, c, d, e, f, g, h, i, j) x -> (a, b, c, d, e, f, g, h, i, j)

Generic (a, b, c, d, e, f, g, h, i, j, k)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i, j, k) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i, j, k) -> Rep (a, b, c, d, e, f, g, h, i, j, k) x

to :: Rep (a, b, c, d, e, f, g, h, i, j, k) x -> (a, b, c, d, e, f, g, h, i, j, k)

Generic (a, b, c, d, e, f, g, h, i, j, k, l)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i, j, k, l) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i, j, k, l) -> Rep (a, b, c, d, e, f, g, h, i, j, k, l) x

to :: Rep (a, b, c, d, e, f, g, h, i, j, k, l) x -> (a, b, c, d, e, f, g, h, i, j, k, l)

Generic (a, b, c, d, e, f, g, h, i, j, k, l, m)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i, j, k, l, m) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i, j, k, l, m) -> Rep (a, b, c, d, e, f, g, h, i, j, k, l, m) x

to :: Rep (a, b, c, d, e, f, g, h, i, j, k, l, m) x -> (a, b, c, d, e, f, g, h, i, j, k, l, m)

Generic (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i, j, k, l, m, n) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n) -> Rep (a, b, c, d, e, f, g, h, i, j, k, l, m, n) x

to :: Rep (a, b, c, d, e, f, g, h, i, j, k, l, m, n) x -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

Generic (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

Defined in GHC.Generics

Associated Types

type Rep (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) :: Type -> Type

Methods

from :: (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) -> Rep (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) x

to :: Rep (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) x -> (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

class PartialSemigroup a where

A PartialSemigroup is like a Semigroup, but with an operator returning Maybe a rather than a.

For comparison:

(<>)  :: Semigroup a        => a -> a -> a
(<>?) :: PartialSemigroup a => a -> a -> Maybe a

The associativity axiom for partial semigroups

For all x, y, z:

• If x <>? y = Just xy and y <>? z = Just yz, then

  • x <>? yz = xy <>? z.

Relationship to the semigroup associativity axiom

The partial semigroup associativity axiom is a natural adaptation of the semigroup associativity axiom

x <> (y <> z) = (x <> y) <> z

with a slight modification to accommodate situations where <> is undefined. We may gain some insight into the connection between Semigroup and PartialSemigroup by rephrasing the partial semigroup associativity in terms of a partial <> operator thusly:

For all x, y, z:

• If x <> y and y <> z are both defined, then

  • x <> (y <> z) is defined if and only if (x <> y) <> z is defined, and
  • if these things are all defined, then the axiom for total semigroups x <> (y <> z) = (x <> y) <> z must hold.

Methods

(<>?) :: a -> a -> Maybe a infixr 6

Instances

PartialSemigroup ()

Defined in Data.PartialSemigroup

Methods

(<>?) :: () -> () -> Maybe ()

PartialSemigroup a => PartialSemigroup (ZipList a)

partialZip

Defined in Data.PartialSemigroup

Methods

(<>?) :: ZipList a -> ZipList a -> Maybe (ZipList a)

PartialSemigroup a => PartialSemigroup (Identity a)

Defined in Data.PartialSemigroup

Methods

(<>?) :: Identity a -> Identity a -> Maybe (Identity a)

Num a => PartialSemigroup (Product a)

Defined in Data.PartialSemigroup

Methods

(<>?) :: Product a -> Product a -> Maybe (Product a)

Num a => PartialSemigroup (Sum a)

Defined in Data.PartialSemigroup

Methods

(<>?) :: Sum a -> Sum a -> Maybe (Sum a)

PartialSemigroup (AtMostOne a)

Defined in Data.PartialSemigroup

Methods

(<>?) :: AtMostOne a -> AtMostOne a -> Maybe (AtMostOne a)

PartialSemigroup (One a)

Defined in Data.PartialSemigroup

Methods

(<>?) :: One a -> One a -> Maybe (One a)

Semigroup a => PartialSemigroup (Total a)

Defined in Data.PartialSemigroup

Methods

(<>?) :: Total a -> Total a -> Maybe (Total a)

PartialSemigroup [a]

Defined in Data.PartialSemigroup

Methods

(<>?) :: [a] -> [a] -> Maybe [a]

(PartialSemigroup a, PartialSemigroup b) => PartialSemigroup (Either a b)

Defined in Data.PartialSemigroup

Methods

(<>?) :: Either a b -> Either a b -> Maybe (Either a b)

PartialSemigroup a => PartialSemigroup (AppendLeft a b)

Defined in Data.PartialSemigroup

Methods

(<>?) :: AppendLeft a b -> AppendLeft a b -> Maybe (AppendLeft a b)

PartialSemigroup b => PartialSemigroup (AppendRight a b)

Defined in Data.PartialSemigroup

Methods

(<>?) :: AppendRight a b -> AppendRight a b -> Maybe (AppendRight a b)

(PartialSemigroup a, PartialSemigroup b) => PartialSemigroup (a, b)

Defined in Data.PartialSemigroup

Methods

(<>?) :: (a, b) -> (a, b) -> Maybe (a, b)

(PartialSemigroup a, PartialSemigroup b, PartialSemigroup c) => PartialSemigroup (a, b, c)

Defined in Data.PartialSemigroup

Methods

(<>?) :: (a, b, c) -> (a, b, c) -> Maybe (a, b, c)