Data.Tuple.Compat

This uses the OneTuple compatibility library to backport Solo to old versions of GHC. Note that OneTuple makes use of pattern synonyms, which cannot be defined on pre-7.8 versions of GHC. As such, it is not feasible to backport the Solo data constructor on pre-7.8 versions of GHC, as OneTuple defines this as a pattern synonym.

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 -> (a)

Instances

Foldable Solo

Since: base-4.15

Defined in 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

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

Traversable Solo

Since: base-4.15

Defined in 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)

Applicative Solo

Since: base-4.15

Defined in GHC.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.Base

Methods

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

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

Monad Solo

Since: base-4.15

Defined in GHC.Base

Methods

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

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

return :: a -> Solo a

Monoid a => Monoid (a)

Since: base-4.15

Defined in GHC.Base

Methods

mempty :: (a)

mappend :: (a) -> (a) -> (a)

mconcat :: [(a)] -> (a)

Semigroup a => Semigroup (a)

Since: base-4.15

Defined in GHC.Base

Methods

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

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

stimes :: Integral b => b -> (a) -> (a)

Bounded a => Bounded (a)

Defined in GHC.Enum

Methods

minBound :: (a)

maxBound :: (a)

Enum a => Enum (a)

Defined in GHC.Enum

Methods

succ :: (a) -> (a)

pred :: (a) -> (a)

toEnum :: Int -> (a)

fromEnum :: (a) -> Int

enumFrom :: (a) -> [(a)]

enumFromThen :: (a) -> (a) -> [(a)]

enumFromTo :: (a) -> (a) -> [(a)]

enumFromThenTo :: (a) -> (a) -> (a) -> [(a)]

Read a => Read (a)

Since: base-4.15

Defined in GHC.Read

Methods

readsPrec :: Int -> ReadS (a)

readList :: ReadS [(a)]

readPrec :: ReadPrec (a)

readListPrec :: ReadPrec [(a)]

Show a => Show (a)

Since: base-4.15

Defined in GHC.Show

Methods

showsPrec :: Int -> (a) -> ShowS

show :: (a) -> String

showList :: [(a)] -> ShowS

Eq a => Eq (a)

Defined in GHC.Classes

Methods

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

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

Ord a => Ord (a)

Defined in GHC.Classes

Methods

compare :: (a) -> (a) -> Ordering

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

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

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

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

max :: (a) -> (a) -> (a)

min :: (a) -> (a) -> (a)

getSolo :: (a) -> a

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

curry converts 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.