Relude.Bool.Reexport

Reexports functions to work with Bool type.

Documentation

guard :: Alternative f => Bool -> f ()

Conditional failure of Alternative computations. Defined by

guard True  = pure ()
guard False = empty

Examples

Common uses of guard include conditionally signaling an error in an error monad and conditionally rejecting the current choice in an Alternative-based parser.

As an example of signaling an error in the error monad Maybe, consider a safe division function safeDiv x y that returns Nothing when the denominator y is zero and Just (x `div` y) otherwise. For example:

>>> safeDiv 4 0
Nothing
>>> safeDiv 4 2
Just 2

A definition of safeDiv using guards, but not guard:

safeDiv :: Int -> Int -> Maybe Int
safeDiv x y | y /= 0    = Just (x `div` y)
            | otherwise = Nothing

A definition of safeDiv using guard and Monad do-notation:

safeDiv :: Int -> Int -> Maybe Int
safeDiv x y = do
  guard (y /= 0)
  return (x `div` y)

unless :: Applicative f => Bool -> f () -> f ()

The reverse of when.

when :: Applicative f => Bool -> f () -> f ()

Conditional execution of Applicative expressions. For example,

when debug (putStrLn "Debugging")

will output the string Debugging if the Boolean value debug is True, and otherwise do nothing.

otherwise :: Bool

otherwise is defined as the value True. It helps to make guards more readable. eg.

 f x | x < 0     = ...
     | otherwise = ...

data Bool

Constructors

False

True

Instances

Bounded Bool

Since: base-2.1

Defined in GHC.Enum

Methods

minBound :: Bool

maxBound :: Bool

Enum Bool

Since: base-2.1

Defined in GHC.Enum

Methods

succ :: Bool -> Bool

pred :: Bool -> Bool

toEnum :: Int -> Bool

fromEnum :: Bool -> Int

enumFrom :: Bool -> [Bool]

enumFromThen :: Bool -> Bool -> [Bool]

enumFromTo :: Bool -> Bool -> [Bool]

enumFromThenTo :: Bool -> Bool -> Bool -> [Bool]

Eq Bool

Defined in GHC.Classes

Methods

(==) :: Bool -> Bool -> Bool

(/=) :: Bool -> Bool -> Bool

Data Bool

Since: base-4.0.0.0

Defined in Data.Data

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Bool -> c Bool

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Bool

toConstr :: Bool -> Constr

dataTypeOf :: Bool -> DataType

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Bool)

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Bool)

gmapT :: (forall b. Data b => b -> b) -> Bool -> Bool

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Bool -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Bool -> r

gmapQ :: (forall d. Data d => d -> u) -> Bool -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> Bool -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Bool -> m Bool

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Bool -> m Bool

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Bool -> m Bool

Ord Bool

Defined in GHC.Classes

Methods

compare :: Bool -> Bool -> Ordering

(<) :: Bool -> Bool -> Bool

(<=) :: Bool -> Bool -> Bool

(>) :: Bool -> Bool -> Bool

(>=) :: Bool -> Bool -> Bool

max :: Bool -> Bool -> Bool

min :: Bool -> Bool -> Bool

Read Bool

Since: base-2.1

Defined in GHC.Read

Methods

readsPrec :: Int -> ReadS Bool

readList :: ReadS [Bool]

readPrec :: ReadPrec Bool

readListPrec :: ReadPrec [Bool]

Show Bool

Since: base-2.1

Defined in GHC.Show

Methods

showsPrec :: Int -> Bool -> ShowS

show :: Bool -> String

showList :: [Bool] -> ShowS

Ix Bool

Since: base-2.1

Defined in GHC.Arr

Methods

range :: (Bool, Bool) -> [Bool]

index :: (Bool, Bool) -> Bool -> Int

unsafeIndex :: (Bool, Bool) -> Bool -> Int

inRange :: (Bool, Bool) -> Bool -> Bool

rangeSize :: (Bool, Bool) -> Int

unsafeRangeSize :: (Bool, Bool) -> Int

Generic Bool

Defined in GHC.Generics

Associated Types

type Rep Bool :: Type -> Type

Methods

from :: Bool -> Rep Bool x

to :: Rep Bool x -> Bool

SingKind Bool

Since: base-4.9.0.0

Defined in GHC.Generics

Associated Types

type DemoteRep Bool :: Type

Methods

fromSing :: Sing a -> DemoteRep Bool

Bits Bool

Interpret Bool as 1-bit bit-field

Since: base-4.7.0.0

Defined in Data.Bits

Methods

(.&.) :: Bool -> Bool -> Bool

(.|.) :: Bool -> Bool -> Bool

xor :: Bool -> Bool -> Bool

complement :: Bool -> Bool

shift :: Bool -> Int -> Bool

rotate :: Bool -> Int -> Bool

zeroBits :: Bool

bit :: Int -> Bool

setBit :: Bool -> Int -> Bool

clearBit :: Bool -> Int -> Bool

complementBit :: Bool -> Int -> Bool

testBit :: Bool -> Int -> Bool

bitSizeMaybe :: Bool -> Maybe Int

bitSize :: Bool -> Int

isSigned :: Bool -> Bool

shiftL :: Bool -> Int -> Bool

unsafeShiftL :: Bool -> Int -> Bool

shiftR :: Bool -> Int -> Bool

unsafeShiftR :: Bool -> Int -> Bool

rotateL :: Bool -> Int -> Bool

rotateR :: Bool -> Int -> Bool

popCount :: Bool -> Int

FiniteBits Bool

Since: base-4.7.0.0

Defined in Data.Bits

Methods

finiteBitSize :: Bool -> Int

countLeadingZeros :: Bool -> Int

countTrailingZeros :: Bool -> Int

NFData Bool

Defined in Control.DeepSeq

Methods

rnf :: Bool -> ()

Hashable Bool

Defined in Data.Hashable.Class

Methods

hashWithSalt :: Int -> Bool -> Int

hash :: Bool -> Int

SingI False

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

sing :: Sing False

SingI True

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

sing :: Sing True

type Rep Bool

Since: base-4.6.0.0

Defined in GHC.Generics

type Rep Bool = D1 (MetaData "Bool" "GHC.Types" "ghc-prim" False) (C1 (MetaCons "False" PrefixI False) (U1 :: Type -> Type) :+: C1 (MetaCons "True" PrefixI False) (U1 :: Type -> Type))

data Sing (a :: Bool)

Defined in GHC.Generics

data Sing (a :: Bool) where

• STrue :: forall (a :: Bool). Sing True
• SFalse :: forall (a :: Bool). Sing False

type DemoteRep Bool

Defined in GHC.Generics

type DemoteRep Bool = Bool

bool :: a -> a -> Bool -> a

Case analysis for the Bool type. bool x y p evaluates to x when p is False, and evaluates to y when p is True.

This is equivalent to if p then y else x; that is, one can think of it as an if-then-else construct with its arguments reordered.

Examples

Basic usage:

>>> bool "foo" "bar" True
"bar"
>>> bool "foo" "bar" False
"foo"

Confirm that bool x y p and if p then y else x are equivalent:

>>> let p = True; x = "bar"; y = "foo"
>>> bool x y p == if p then y else x
True
>>> let p = False
>>> bool x y p == if p then y else x
True

Since: base-4.7.0.0

(&&) :: Bool -> Bool -> Bool infixr 3

Boolean "and"

(||) :: Bool -> Bool -> Bool infixr 2

Boolean "or"

not :: Bool -> Bool

Boolean "not"