Data.Tuple

Functions associated with the tuple data types.

Documentation

data Solo a

Solo is the canonical lifted 1-tuple, just like (,) is the canonical lifted 2-tuple (pair) and (,,) is the canonical lifted 3-tuple (triple).

The most important feature of Solo is that it is possible to force its "outside" (usually by pattern matching) without forcing its "inside", because it is defined as a datatype rather than a newtype. One situation where this can be useful is when writing a function to extract a value from a data structure. Suppose you write an implementation of arrays and offer only this function to index into them:

index :: Array a -> Int -> a

Now imagine that someone wants to extract a value from an array and store it in a lazy-valued finite map/dictionary:

insert "hello" (arr index 12) m

This can actually lead to a space leak. The value is not actually extracted from the array until that value (now buried in a map) is forced. That means the entire array may be kept live by just that value! Often, the solution is to use a strict map, or to force the value before storing it, but for some purposes that's undesirable.

One common solution is to include an indexing function that can produce its result in an arbitrary Applicative context:

indexA :: Applicative f => Array a -> Int -> f a

When using indexA in a pure context, Solo serves as a handy Applicative functor to hold the result. You could write a non-leaky version of the above example thus:

case arr indexA 12 of
  Solo a -> insert "hello" a m

While such simple extraction functions are the most common uses for unary tuples, they can also be useful for fine-grained control of strict-spined data structure traversals, and for unifying the implementations of lazy and strict mapping functions.

Constructors

MkSolo a

Bundled Patterns

pattern Solo :: a -> Solo a

Instances

MonadZip Solo

Since: base-4.15.0.0

Defined in Control.Monad.Zip

Methods

mzip :: Solo a -> Solo b -> Solo (a, b)

mzipWith :: (a -> b -> c) -> Solo a -> Solo b -> Solo c

munzip :: Solo (a, b) -> (Solo a, Solo b)

Foldable1 Solo

Since: base-4.18.0.0

Defined in Data.Foldable1

Methods

fold1 :: Semigroup m => Solo m -> m

foldMap1 :: Semigroup m => (a -> m) -> Solo a -> m

foldMap1' :: Semigroup m => (a -> m) -> Solo a -> m

toNonEmpty :: Solo a -> NonEmpty a

maximum :: Ord a => Solo a -> a

minimum :: Ord a => Solo a -> a

head :: Solo a -> a

last :: Solo a -> a

foldrMap1 :: (a -> b) -> (a -> b -> b) -> Solo a -> b

foldlMap1' :: (a -> b) -> (b -> a -> b) -> Solo a -> b

foldlMap1 :: (a -> b) -> (b -> a -> b) -> Solo a -> b

foldrMap1' :: (a -> b) -> (a -> b -> b) -> Solo a -> b

Eq1 Solo

Since: base-4.15

Defined in Data.Functor.Classes

Methods

liftEq :: (a -> b -> Bool) -> Solo a -> Solo b -> Bool

Ord1 Solo

Since: base-4.15

Defined in Data.Functor.Classes

Methods

liftCompare :: (a -> b -> Ordering) -> Solo a -> Solo b -> Ordering

Read1 Solo

Since: base-4.15

Defined in Data.Functor.Classes

Methods

liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Solo a)

liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Solo a]

liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (Solo a)

liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [Solo a]

Show1 Solo

Since: base-4.15

Defined in Data.Functor.Classes

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Solo a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Solo a] -> ShowS

Applicative Solo

Since: base-4.15

Defined in GHC.Internal.Base

Methods

pure :: a -> Solo a

(<*>) :: Solo (a -> b) -> Solo a -> Solo b

liftA2 :: (a -> b -> c) -> Solo a -> Solo b -> Solo c

(*>) :: Solo a -> Solo b -> Solo b

(<*) :: Solo a -> Solo b -> Solo a

Functor Solo

Since: base-4.15

Defined in GHC.Internal.Base

Methods

fmap :: (a -> b) -> Solo a -> Solo b

(<$) :: a -> Solo b -> Solo a

Monad Solo

Since: base-4.15

Defined in GHC.Internal.Base

Methods

(>>=) :: Solo a -> (a -> Solo b) -> Solo b

(>>) :: Solo a -> Solo b -> Solo b

return :: a -> Solo a

MonadFix Solo

Since: base-4.15

Defined in GHC.Internal.Control.Monad.Fix

Methods

mfix :: (a -> Solo a) -> Solo a

Foldable Solo

Since: base-4.15

Defined in GHC.Internal.Data.Foldable

Methods

fold :: Monoid m => Solo m -> m

foldMap :: Monoid m => (a -> m) -> Solo a -> m

foldMap' :: Monoid m => (a -> m) -> Solo a -> m

foldr :: (a -> b -> b) -> b -> Solo a -> b

foldr' :: (a -> b -> b) -> b -> Solo a -> b

foldl :: (b -> a -> b) -> b -> Solo a -> b

foldl' :: (b -> a -> b) -> b -> Solo a -> b

foldr1 :: (a -> a -> a) -> Solo a -> a

foldl1 :: (a -> a -> a) -> Solo a -> a

toList :: Solo a -> [a]

null :: Solo a -> Bool

length :: Solo a -> Int

elem :: Eq a => a -> Solo a -> Bool

maximum :: Ord a => Solo a -> a

minimum :: Ord a => Solo a -> a

sum :: Num a => Solo a -> a

product :: Num a => Solo a -> a

Traversable Solo

Since: base-4.15

Defined in GHC.Internal.Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Solo a -> f (Solo b)

sequenceA :: Applicative f => Solo (f a) -> f (Solo a)

mapM :: Monad m => (a -> m b) -> Solo a -> m (Solo b)

sequence :: Monad m => Solo (m a) -> m (Solo a)

Generic1 Solo

Defined in GHC.Internal.Generics

Associated Types

type Rep1 Solo

Since: base-4.15

Defined in GHC.Internal.Generics

type Rep1 Solo = D1 ('MetaData "Solo" "GHC.Tuple" "ghc-prim" 'False) (C1 ('MetaCons "MkSolo" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1))

Methods

from1 :: Solo a -> Rep1 Solo a

to1 :: Rep1 Solo a -> Solo a

Monoid a => Monoid (Solo a)

Since: base-4.15

Defined in GHC.Internal.Base

Methods

mempty :: Solo a

mappend :: Solo a -> Solo a -> Solo a

mconcat :: [Solo a] -> Solo a

Semigroup a => Semigroup (Solo a)

Since: base-4.15

Defined in GHC.Internal.Base

Methods

(<>) :: Solo a -> Solo a -> Solo a

sconcat :: NonEmpty (Solo a) -> Solo a

stimes :: Integral b => b -> Solo a -> Solo a

Data a => Data (Solo a)

Since: base-4.15

Defined in GHC.Internal.Data.Data

Methods

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

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

toConstr :: Solo a -> Constr

dataTypeOf :: Solo a -> DataType

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

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

gmapT :: (forall b. Data b => b -> b) -> Solo a -> Solo a

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

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

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

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

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

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

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

Bounded a => Bounded (Solo a)

Defined in GHC.Internal.Enum

Methods

minBound :: Solo a

maxBound :: Solo a

Enum a => Enum (Solo a)

Defined in GHC.Internal.Enum

Methods

succ :: Solo a -> Solo a

pred :: Solo a -> Solo a

toEnum :: Int -> Solo a

fromEnum :: Solo a -> Int

enumFrom :: Solo a -> [Solo a]

enumFromThen :: Solo a -> Solo a -> [Solo a]

enumFromTo :: Solo a -> Solo a -> [Solo a]

enumFromThenTo :: Solo a -> Solo a -> Solo a -> [Solo a]

Generic (Solo a)

Defined in GHC.Internal.Generics

Associated Types

type Rep (Solo a)

Since: base-4.15

Defined in GHC.Internal.Generics

type Rep (Solo a) = D1 ('MetaData "Solo" "GHC.Tuple" "ghc-prim" 'False) (C1 ('MetaCons "MkSolo" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))

Methods

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

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

Ix a => Ix (Solo a)

Defined in GHC.Internal.Ix

Methods

range :: (Solo a, Solo a) -> [Solo a]

index :: (Solo a, Solo a) -> Solo a -> Int

unsafeIndex :: (Solo a, Solo a) -> Solo a -> Int

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

rangeSize :: (Solo a, Solo a) -> Int

unsafeRangeSize :: (Solo a, Solo a) -> Int

Read a => Read (Solo a)

Since: base-4.15

Defined in GHC.Internal.Read

Methods

readsPrec :: Int -> ReadS (Solo a)

readList :: ReadS [Solo a]

readPrec :: ReadPrec (Solo a)

readListPrec :: ReadPrec [Solo a]

Show a => Show (Solo a)

Since: base-4.15

Defined in GHC.Internal.Show

Methods

showsPrec :: Int -> Solo a -> ShowS

show :: Solo a -> String

showList :: [Solo a] -> ShowS

Eq a => Eq (Solo a)

Defined in GHC.Classes

Methods

(==) :: Solo a -> Solo a -> Bool

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

Ord a => Ord (Solo a)

Defined in GHC.Classes

Methods

compare :: Solo a -> Solo a -> Ordering

(<) :: Solo a -> Solo a -> Bool

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

(>) :: Solo a -> Solo a -> Bool

(>=) :: Solo a -> Solo a -> Bool

max :: Solo a -> Solo a -> Solo a

min :: Solo a -> Solo a -> Solo a

type Rep1 Solo

Since: base-4.15

Defined in GHC.Internal.Generics

type Rep1 Solo = D1 ('MetaData "Solo" "GHC.Tuple" "ghc-prim" 'False) (C1 ('MetaCons "MkSolo" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1))

type Rep (Solo a)

Since: base-4.15

Defined in GHC.Internal.Generics

type Rep (Solo a) = D1 ('MetaData "Solo" "GHC.Tuple" "ghc-prim" 'False) (C1 ('MetaCons "MkSolo" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a)))

getSolo :: Solo a -> a

Extract the value from a Solo. Very often, values should be extracted directly using pattern matching, to control just what gets evaluated when. getSolo is for convenience in situations where that is not the case:

When the result is passed to a strict function, it makes no difference whether the pattern matching is done on the "outside" or on the "inside":

Data.Set.insert (getSolo sol) set === case sol of Solo v -> Data.Set.insert v set

A traversal may be performed in Solo in order to control evaluation internally, while using getSolo to extract the final result. A strict mapping function, for example, could be defined

map' :: Traversable t => (a -> b) -> t a -> t b
map' f = getSolo . traverse ((Solo $!) . f)

fst :: (a, b) -> a

Extract the first component of a pair.

snd :: (a, b) -> b

Extract the second component of a pair.

curry :: ((a, b) -> c) -> a -> b -> c

Convert an uncurried function to a curried function.

Examples

>>> curry fst 1 2
1

uncurry :: (a -> b -> c) -> (a, b) -> c

uncurry converts a curried function to a function on pairs.

Examples

>>> uncurry (+) (1,2)
3

>>> uncurry ($) (show, 1)
"1"

>>> map (uncurry max) [(1,2), (3,4), (6,8)]
[2,4,8]

swap :: (a, b) -> (b, a)

Swap the components of a pair.