Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
Documentation
The Maybe
type encapsulates an optional value. A value of type
either contains a value of type Maybe
aa
(represented as
),
or it is empty (represented as Just
aNothing
). Using Maybe
is a good way to
deal with errors or exceptional cases without resorting to drastic
measures such as error
.
The Maybe
type is also a monad. It is a simple kind of error
monad, where all errors are represented by Nothing
. A richer
error monad can be built using the Either
type.
Instances
FromJSON1 Maybe | |
Defined in Data.Aeson.Types.FromJSON | |
ToJSON1 Maybe | |
Defined in Data.Aeson.Types.ToJSON liftToJSON ∷ (a → Bool) → (a → Value) → ([a] → Value) → Maybe a → Value Source # liftToJSONList ∷ (a → Bool) → (a → Value) → ([a] → Value) → [Maybe a] → Value Source # liftToEncoding ∷ (a → Bool) → (a → Encoding) → ([a] → Encoding) → Maybe a → Encoding Source # liftToEncodingList ∷ (a → Bool) → (a → Encoding) → ([a] → Encoding) → [Maybe a] → Encoding Source # | |
MonadFail Maybe | Since: base-4.9.0.0 |
Foldable Maybe | Since: base-2.1 |
Defined in Data.Foldable fold ∷ Monoid m ⇒ Maybe m → m Source # foldMap ∷ Monoid m ⇒ (a → m) → Maybe a → m Source # foldMap' ∷ Monoid m ⇒ (a → m) → Maybe a → m Source # foldr ∷ (a → b → b) → b → Maybe a → b Source # foldr' ∷ (a → b → b) → b → Maybe a → b Source # foldl ∷ (b → a → b) → b → Maybe a → b Source # foldl' ∷ (b → a → b) → b → Maybe a → b Source # foldr1 ∷ (a → a → a) → Maybe a → a Source # foldl1 ∷ (a → a → a) → Maybe a → a Source # toList ∷ Maybe a → [a] Source # null ∷ Maybe a → Bool Source # length ∷ Maybe a → Int Source # elem ∷ Eq a ⇒ a → Maybe a → Bool Source # maximum ∷ Ord a ⇒ Maybe a → a Source # minimum ∷ Ord a ⇒ Maybe a → a Source # | |
Traversable Maybe | Since: base-2.1 |
Alternative Maybe | Picks the leftmost Since: base-2.1 |
Applicative Maybe | Since: base-2.1 |
Functor Maybe | Since: base-2.1 |
Monad Maybe | Since: base-2.1 |
MonadPlus Maybe | Picks the leftmost Since: base-2.1 |
MonadFailure Maybe | |
NFData1 Maybe | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
Hashable1 Maybe | |
Defined in Data.Hashable.Class | |
Applicative Maybe Source # | |
Foldable Maybe Source # | |
Defined in PlutusTx.Foldable | |
Functor Maybe Source # | |
Traversable Maybe Source # | |
Defined in PlutusTx.Traversable | |
Generic1 Maybe | |
FoldableWithIndex () Maybe | |
FunctorWithIndex () Maybe | |
TraversableWithIndex () Maybe | |
Defined in WithIndex itraverse ∷ Applicative f ⇒ (() → a → f b) → Maybe a → f (Maybe b) | |
MonadBaseControl Maybe Maybe | |
Defined in Control.Monad.Trans.Control type StM Maybe a | |
MonadError () Maybe | Since: mtl-2.2.2 |
Defined in Control.Monad.Error.Class throwError ∷ () → Maybe a Source # | |
(Typeable DefaultUni a, Lift DefaultUni a) ⇒ Lift DefaultUni (Maybe a) Source # | |
Defined in PlutusTx.Lift.Instances lift ∷ Maybe a → RTCompile DefaultUni fun (Term TyName Name DefaultUni fun ()) Source # | |
PrettyBy config a ⇒ DefaultPrettyBy config (Maybe a) | |
Defined in Text.PrettyBy.Internal defaultPrettyBy ∷ config → Maybe a → Doc ann Source # defaultPrettyListBy ∷ config → [Maybe a] → Doc ann Source # | |
PrettyDefaultBy config (Maybe a) ⇒ PrettyBy config (Maybe a) | By default a
|
Lift a ⇒ Lift (Maybe a ∷ Type) | |
FromJSON a ⇒ FromJSON (Maybe a) | |
ToJSON a ⇒ ToJSON (Maybe a) | |
Graph g ⇒ Graph (Maybe g) | |
Preorder g ⇒ Preorder (Maybe g) | |
Defined in Algebra.Graph.Class | |
Reflexive g ⇒ Reflexive (Maybe g) | |
Defined in Algebra.Graph.Class | |
Transitive g ⇒ Transitive (Maybe g) | |
Defined in Algebra.Graph.Class | |
Undirected g ⇒ Undirected (Maybe g) | |
Defined in Algebra.Graph.Class | |
Data a ⇒ Data (Maybe a) | Since: base-4.0.0.0 |
Defined in Data.Data gfoldl ∷ (∀ d b. Data d ⇒ c (d → b) → d → c b) → (∀ g. g → c g) → Maybe a → c (Maybe a) Source # gunfold ∷ (∀ b r. Data b ⇒ c (b → r) → c r) → (∀ r. r → c r) → Constr → c (Maybe a) Source # toConstr ∷ Maybe a → Constr Source # dataTypeOf ∷ Maybe a → DataType Source # dataCast1 ∷ Typeable t ⇒ (∀ d. Data d ⇒ c (t d)) → Maybe (c (Maybe a)) Source # dataCast2 ∷ Typeable t ⇒ (∀ d e. (Data d, Data e) ⇒ c (t d e)) → Maybe (c (Maybe a)) Source # gmapT ∷ (∀ b. Data b ⇒ b → b) → Maybe a → Maybe a Source # gmapQl ∷ (r → r' → r) → r → (∀ d. Data d ⇒ d → r') → Maybe a → r Source # gmapQr ∷ ∀ r r'. (r' → r → r) → r → (∀ d. Data d ⇒ d → r') → Maybe a → r Source # gmapQ ∷ (∀ d. Data d ⇒ d → u) → Maybe a → [u] Source # gmapQi ∷ Int → (∀ d. Data d ⇒ d → u) → Maybe a → u Source # gmapM ∷ Monad m ⇒ (∀ d. Data d ⇒ d → m d) → Maybe a → m (Maybe a) Source # gmapMp ∷ MonadPlus m ⇒ (∀ d. Data d ⇒ d → m d) → Maybe a → m (Maybe a) Source # gmapMo ∷ MonadPlus m ⇒ (∀ d. Data d ⇒ d → m d) → Maybe a → m (Maybe a) Source # | |
Semigroup a ⇒ Monoid (Maybe a) | Lift a semigroup into Since 4.11.0: constraint on inner Since: base-2.1 |
Semigroup a ⇒ Semigroup (Maybe a) | Since: base-4.9.0.0 |
Generic (Maybe a) | |
SingKind a ⇒ SingKind (Maybe a) | Since: base-4.9.0.0 |
Defined in GHC.Generics type DemoteRep (Maybe a) | |
Read a ⇒ Read (Maybe a) | Since: base-2.1 |
Show a ⇒ Show (Maybe a) | Since: base-2.1 |
Default (Maybe a) | |
Defined in Data.Default.Class | |
NFData a ⇒ NFData (Maybe a) | |
Defined in Control.DeepSeq | |
Eq a ⇒ Eq (Maybe a) | Since: base-2.1 |
Ord a ⇒ Ord (Maybe a) | Since: base-2.1 |
Defined in GHC.Maybe | |
Hashable a ⇒ Hashable (Maybe a) | |
At (Maybe a) | |
Ixed (Maybe a) | |
Defined in Control.Lens.At | |
AsEmpty (Maybe a) | |
Defined in Control.Lens.Empty | |
MonoFoldable (Maybe a) | |
Defined in Data.MonoTraversable ofoldMap ∷ Monoid m ⇒ (Element (Maybe a) → m) → Maybe a → m Source # ofoldr ∷ (Element (Maybe a) → b → b) → b → Maybe a → b Source # ofoldl' ∷ (a0 → Element (Maybe a) → a0) → a0 → Maybe a → a0 Source # otoList ∷ Maybe a → [Element (Maybe a)] Source # oall ∷ (Element (Maybe a) → Bool) → Maybe a → Bool Source # oany ∷ (Element (Maybe a) → Bool) → Maybe a → Bool Source # onull ∷ Maybe a → Bool Source # olength ∷ Maybe a → Int Source # olength64 ∷ Maybe a → Int64 Source # ocompareLength ∷ Integral i ⇒ Maybe a → i → Ordering Source # otraverse_ ∷ Applicative f ⇒ (Element (Maybe a) → f b) → Maybe a → f () Source # ofor_ ∷ Applicative f ⇒ Maybe a → (Element (Maybe a) → f b) → f () Source # omapM_ ∷ Applicative m ⇒ (Element (Maybe a) → m ()) → Maybe a → m () Source # oforM_ ∷ Applicative m ⇒ Maybe a → (Element (Maybe a) → m ()) → m () Source # ofoldlM ∷ Monad m ⇒ (a0 → Element (Maybe a) → m a0) → a0 → Maybe a → m a0 Source # ofoldMap1Ex ∷ Semigroup m ⇒ (Element (Maybe a) → m) → Maybe a → m Source # ofoldr1Ex ∷ (Element (Maybe a) → Element (Maybe a) → Element (Maybe a)) → Maybe a → Element (Maybe a) Source # ofoldl1Ex' ∷ (Element (Maybe a) → Element (Maybe a) → Element (Maybe a)) → Maybe a → Element (Maybe a) Source # headEx ∷ Maybe a → Element (Maybe a) Source # lastEx ∷ Maybe a → Element (Maybe a) Source # unsafeHead ∷ Maybe a → Element (Maybe a) Source # unsafeLast ∷ Maybe a → Element (Maybe a) Source # maximumByEx ∷ (Element (Maybe a) → Element (Maybe a) → Ordering) → Maybe a → Element (Maybe a) Source # minimumByEx ∷ (Element (Maybe a) → Element (Maybe a) → Ordering) → Maybe a → Element (Maybe a) Source # | |
MonoFunctor (Maybe a) | |
MonoPointed (Maybe a) | |
MonoTraversable (Maybe a) | |
HasBlueprintDefinition a ⇒ HasBlueprintDefinition (Maybe a) Source # | |
Defined in PlutusTx.Blueprint.Definition.Unroll | |
Eq a ⇒ Eq (Maybe a) Source # | |
FromData a ⇒ FromData (Maybe a) Source # | |
Defined in PlutusTx.IsData.Instances fromBuiltinData ∷ BuiltinData → Maybe (Maybe a) Source # | |
ToData a ⇒ ToData (Maybe a) Source # | |
Defined in PlutusTx.IsData.Instances toBuiltinData ∷ Maybe a → BuiltinData Source # | |
UnsafeFromData a ⇒ UnsafeFromData (Maybe a) Source # | |
Defined in PlutusTx.IsData.Instances | |
Semigroup a ⇒ Monoid (Maybe a) Source # | |
Defined in PlutusTx.Monoid | |
Ord a ⇒ Ord (Maybe a) Source # | |
Defined in PlutusTx.Ord | |
Semigroup a ⇒ Semigroup (Maybe a) Source # | |
Show a ⇒ Show (Maybe a) Source # | |
Pretty a ⇒ Pretty (Maybe a) | Ignore
|
Corecursive (Maybe a) | |
Defined in Data.Functor.Foldable embed ∷ Base (Maybe a) (Maybe a) → Maybe a Source # ana ∷ (a0 → Base (Maybe a) a0) → a0 → Maybe a Source # apo ∷ (a0 → Base (Maybe a) (Either (Maybe a) a0)) → a0 → Maybe a Source # postpro ∷ Recursive (Maybe a) ⇒ (∀ b. Base (Maybe a) b → Base (Maybe a) b) → (a0 → Base (Maybe a) a0) → a0 → Maybe a Source # gpostpro ∷ (Recursive (Maybe a), Monad m) ⇒ (∀ b. m (Base (Maybe a) b) → Base (Maybe a) (m b)) → (∀ c. Base (Maybe a) c → Base (Maybe a) c) → (a0 → Base (Maybe a) (m a0)) → a0 → Maybe a Source # | |
Recursive (Maybe a) | |
Defined in Data.Functor.Foldable project ∷ Maybe a → Base (Maybe a) (Maybe a) Source # cata ∷ (Base (Maybe a) a0 → a0) → Maybe a → a0 Source # para ∷ (Base (Maybe a) (Maybe a, a0) → a0) → Maybe a → a0 Source # gpara ∷ (Corecursive (Maybe a), Comonad w) ⇒ (∀ b. Base (Maybe a) (w b) → w (Base (Maybe a) b)) → (Base (Maybe a) (EnvT (Maybe a) w a0) → a0) → Maybe a → a0 Source # prepro ∷ Corecursive (Maybe a) ⇒ (∀ b. Base (Maybe a) b → Base (Maybe a) b) → (Base (Maybe a) a0 → a0) → Maybe a → a0 Source # gprepro ∷ (Corecursive (Maybe a), Comonad w) ⇒ (∀ b. Base (Maybe a) (w b) → w (Base (Maybe a) b)) → (∀ c. Base (Maybe a) c → Base (Maybe a) c) → (Base (Maybe a) (w a0) → a0) → Maybe a → a0 Source # | |
Serialise a ⇒ Serialise (Maybe a) | Since: serialise-0.2.0.0 |
Pretty a ⇒ Pretty (Maybe a) | |
Defined in Text.PrettyPrint.Annotated.WL prettyList ∷ [Maybe a] → Doc b | |
(HasBlueprintDefinition a, HasSchemaDefinition a referencedTypes) ⇒ HasBlueprintSchema (Maybe a) referencedTypes Source # | |
Defined in PlutusTx.IsData.Instances | |
SingI ('Nothing ∷ Maybe a) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Each (Maybe a) (Maybe b) a b | |
Defined in Control.Lens.Each | |
Each (Maybe a) (Maybe b) a b | |
SingI a2 ⇒ SingI ('Just a2 ∷ Maybe a1) | Since: base-4.9.0.0 |
Defined in GHC.Generics | |
Typeable DefaultUni Maybe Source # | |
Defined in PlutusTx.Lift.Instances typeRep ∷ Proxy Maybe → RTCompile DefaultUni fun (Type TyName DefaultUni ()) Source # | |
type Failure Maybe | |
Defined in Basement.Monad type Failure Maybe = () | |
type Rep1 Maybe | Since: base-4.6.0.0 |
type StM Maybe a | |
Defined in Control.Monad.Trans.Control type StM Maybe a = a | |
type Vertex (Maybe g) | |
Defined in Algebra.Graph.Class | |
type DemoteRep (Maybe a) | |
Defined in GHC.Generics | |
type Rep (Maybe a) | Since: base-4.6.0.0 |
Defined in GHC.Generics | |
data Sing (b ∷ Maybe a) | |
type Index (Maybe a) | |
Defined in Control.Lens.At type Index (Maybe a) = () | |
type IxValue (Maybe a) | |
Defined in Control.Lens.At type IxValue (Maybe a) = a | |
type Element (Maybe a) | |
Defined in Data.MonoTraversable | |
type Unroll (Maybe a) Source # | |
type Base (Maybe a) | Example boring stub for non-recursive data types |
isJust ∷ Maybe a → Bool Source #
Check if a Maybe
a
is Just a
>>>
isJust Nothing
False>>>
isJust (Just "plutus")
True
isNothing ∷ Maybe a → Bool Source #
Check if a Maybe
a
is Nothing
>>>
isNothing Nothing
True>>>
isNothing (Just "plutus")
False