Module Prelude.Maybe

Provides functions and instances for the Maybe type.

Compatible with the Haskell 2010 Data.Maybe module.

Imports

• import Prelude.PreludeBase as PreludeBase
• import Prelude.PreludeList as PreludeList
• import Prelude.PreludeMonad as PreludeMonad
• import Control.Semigroupoid as Semigroupoid

Table of Content

• Definitions

  isJust ∷ Maybe 𝖆 → Bool

  isNothing ∷ Maybe 𝖆 → Bool

  fromMaybe ∷ 𝖆 → Maybe 𝖆 → 𝖆

  unJust ∷ Maybe 𝖆 → 𝖆

  catMaybes ∷ ListSource 𝖇 ⇒ 𝖇 (Maybe 𝖆) → [𝖆]

  mapMaybe ∷ (𝖇→Maybe 𝖆) → [𝖇] → [𝖆]

  listToMaybe ∷ ListSource 𝖇 ⇒ 𝖇 𝖆 → Maybe 𝖆

  maybeToList ∷ Maybe a → [a]

• Instances

  instance Applicative Maybe

  instance Eq a ⇒ Eq (Maybe a)

  instance Functor Maybe

  instance ListEmpty Maybe

  instance MonadFail Maybe

  instance MonadPlus Maybe

  instance Monad Maybe

  instance Ord a ⇒ Ord (Maybe a)

• Functions and Values by Type

Definitions

isJust ∷ Maybe 𝖆 → Bool

true if and only if the argument is a Maybe.Just value

isNothing ∷ Maybe 𝖆 → Bool

true if and only if the argument is Maybe.Nothing

This function is preferable over v == Nothing because no Eq constraint is needed.

fromMaybe ∷ 𝖆 → Maybe 𝖆 → 𝖆

fromMaybe d (Just a) returns a and fromMaybe d Nothing returns d

unJust ∷ Maybe 𝖆 → 𝖆

unJust Nothing is undefined whereas unJust (Just a) is a

catMaybes ∷ ListSource 𝖇 ⇒ 𝖇 (Maybe 𝖆) → [𝖆]

The catMaybes function takes a list of Maybes and returns a list of all the Maybe.Just values.

mapMaybe ∷ (𝖇→Maybe 𝖆) → [𝖇] → [𝖆]

The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe b. If this is Maybe.Nothing, no element is added on to the result list. If it just Maybe.Just b, then b is included in the result list.

listToMaybe ∷ ListSource 𝖇 ⇒ 𝖇 𝖆 → Maybe 𝖆

give the first element of a list or Maybe.Nothing

maybeToList ∷ Maybe a → [a]

convert a Maybe to a single element list or an empty list

Instances

instance Applicative Maybe

Member Functions

*> ∷ Maybe 𝖆 → Maybe 𝖇 → Maybe 𝖇
infixl  4

inherited from Applicative.*>

<* ∷ Maybe 𝖆 → Maybe 𝖇 → Maybe 𝖆
infixl  4

inherited from Applicative.<*

<*> ∷ Maybe (𝖆→𝖇) → Maybe 𝖆 → Maybe 𝖇
infixl  4

pure ∷ 𝖆 → Maybe 𝖆

instance Eq a ⇒ Eq (Maybe a)

Member Functions

!= ∷ Eq 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool
infix  7

inherited from Eq.!=

== ∷ Eq 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool
infix  7

Function generated for derived instance.

hashCode ∷ Eq 𝖆 ⇒ Maybe 𝖆 → Int

Function generated for derived instance.

instance Functor Maybe

Member Functions

fmap ∷ (𝖆 → 𝖇) → Maybe 𝖆 → Maybe 𝖇
infixl  4

instance ListEmpty Maybe

Member Functions

empty ∷ Maybe 𝖆

null ∷ Maybe 𝖆 → Bool

instance MonadFail Maybe

Member Functions

fail ∷ String → Maybe 𝖆

instance MonadPlus Maybe

Member Functions

mplus ∷ Maybe 𝖆 → Maybe 𝖆 → Maybe 𝖆
infixr  13

mzero ∷ Maybe 𝖆

instance Monad Maybe

Member Functions

>> ∷ Maybe 𝖆 → Maybe 𝖇 → Maybe 𝖇
infixl  3

>>= ∷ Maybe 𝖆 → (𝖆 → Maybe 𝖇) → Maybe 𝖇
infixl  3

 Nothing >>= _ = Nothing

 Just a  >>= k = k a   

join ∷ Maybe (Maybe 𝖆) → Maybe 𝖆

inherited from Monad.join

instance Ord a ⇒ Ord (Maybe a)

Member Functions

< ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool
infix  9

inherited from Ord.<

<= ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool
infix  9

inherited from Ord.<=

<=> ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Ordering
infix  8

Function generated for derived instance.

> ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool
infix  9

inherited from Ord.>

>= ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool
infix  9

inherited from Ord.>=

compare ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Ordering
infix  8

inherited from Ord.compare

max ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Maybe 𝖆

inherited from Ord.max

min ∷ Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Maybe 𝖆

inherited from Ord.min

Functions and Values by Type

Maybe (Maybe 𝖆) → Maybe 𝖆

Monad_Maybe.join

Maybe a → [a]

maybeToList

Maybe 𝖆 → Maybe 𝖆 → Maybe 𝖆

MonadPlus_Maybe.mplus

Maybe 𝖆 → Bool

isJust, isNothing, ListEmpty_Maybe.null

Maybe 𝖆 → 𝖆

unJust

String → Maybe 𝖆

MonadFail_Maybe.fail

𝖆 → Maybe 𝖆 → 𝖆

fromMaybe

𝖆 → Maybe 𝖆

Applicative_Maybe.pure

Eq 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool

Eq_Maybe.!=, Eq_Maybe.==

Eq 𝖆 ⇒ Maybe 𝖆 → Int

Eq_Maybe.hashCode

Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Maybe 𝖆

Ord_Maybe.min, Ord_Maybe.max

Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Bool

Ord_Maybe.>=, Ord_Maybe.<, Ord_Maybe.<=, Ord_Maybe.>

Ord 𝖆 ⇒ Maybe 𝖆 → Maybe 𝖆 → Ordering

Ord_Maybe.compare, Ord_Maybe.<=>

Maybe 𝖆

ListEmpty_Maybe.empty, MonadPlus_Maybe.mzero

(𝖆 → 𝖇) → Maybe 𝖆 → Maybe 𝖇

Functor_Maybe.fmap

(𝖇→Maybe 𝖆) → [𝖇] → [𝖆]

mapMaybe

Maybe (𝖆→𝖇) → Maybe 𝖆 → Maybe 𝖇

Applicative_Maybe.<*>

Maybe 𝖆 → (𝖆 → Maybe 𝖇) → Maybe 𝖇

Monad_Maybe.>>=

Maybe 𝖆 → Maybe 𝖇 → Maybe 𝖆

Applicative_Maybe.<*

Maybe 𝖆 → Maybe 𝖇 → Maybe 𝖇

Applicative_Maybe.*>, Monad_Maybe.>>

ListSource 𝖇 ⇒ 𝖇 (Maybe 𝖆) → [𝖆]

catMaybes

ListSource 𝖇 ⇒ 𝖇 𝖆 → Maybe 𝖆

listToMaybe