Data.Tuple.Extra

Extra functions for working with tuples. Some of these functions are available in the Control.Arrow module, but here are available specialised to pairs.

Specialised Arrow functions

first :: (a -> a') -> (a, b) -> (a', b)

Update the first component of a pair.

 first succ (1,"test") == (2,"test")

second :: (b -> b') -> (a, b) -> (a, b')

Update the second component of a pair.

 second reverse (1,"test") == (1,"tset")

(***) :: (a -> a') -> (b -> b') -> (a, b) -> (a', b')

Given two functions, apply one to the first component and one to the second. A specialised version of ***.

 (succ *** reverse) (1,"test") == (2,"tset")

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

Given two functions, apply both to a single argument to form a pair. A specialised version of &&&.

 (succ &&& pred) 1 == (2,0)

More pair operations

dupe :: a -> (a, a)

Duplicate a single value into a pair.

 dupe 12 == (12, 12)

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

Apply a single function to both componenets of a pair.

 both succ (1,2) == (2,3)

Extract from a triple

fst3 :: (a, b, c) -> a

Extract the fst of a triple.

snd3 :: (a, b, c) -> b

Extract the snd of a triple.

thd3 :: (a, b, c) -> c

Extract the final element of a triple.