aivi.pair

Utilities for working with two-element tuples. Pairs are written (A, B) and are the primary way to group two values of potentially different types.

use aivi.pair (
    first
    second
    mapFirst
    mapSecond
    fst
    snd
    swap
    mapFst
    mapSnd
    mapBoth
    fromPair
    toPair
    duplicate
)

At a glance

Canonical pair helpers

Function	Type	Use it for
first	(A, B) -> A	Extract the left item
second	(A, B) -> B	Extract the right item
swap	(A, B) -> (B, A)	Reverse the pair order
mapFirst	(A -> C) -> (A, B) -> (C, B)	Transform only the left item
mapSecond	(B -> C) -> (A, B) -> (A, C)	Transform only the right item
mapBoth	(A -> C) -> (B -> D) -> (A, B) -> (C, D)	Transform both sides with separate functions
fromPair	A -> B -> (A, B)	Build a pair from two values
toPair	A -> B -> (A, B)	Named pairing combinator
duplicate	A -> (A, A)	Put the same value on both sides

Compatibility aliases

Function	Type	Status
fst	(A, B) -> A	Compatibility alias for first
snd	(A, B) -> B	Compatibility alias for second
mapFst	(A -> C) -> (A, B) -> (C, B)	Compatibility alias for mapFirst
mapSnd	(B -> C) -> (A, B) -> (A, C)	Compatibility alias for mapSecond

---

first

Extracts the first element of a pair.

type (Text, Int) -> Text
func getKey = entry =>
    first entry

---

second

Extracts the second element of a pair.

type (Text, Int) -> Int
func getValue = entry =>
    second entry

---

swap

Swaps the two elements of a pair, returning (B, A) from (A, B).

use aivi.pair (swap)

type (Text, Int) -> (Int, Text)
func flipEntry = entry =>
    swap entry

---

mapFirst

Applies a function to the first element, leaving the second unchanged.

use aivi.math (square)

type (Int, Text) -> (Int, Text)
func squareFst = pair =>
    mapFirst square pair

---

mapSecond

Applies a function to the second element, leaving the first unchanged.

use aivi.math (abs)

type (Text, Int) -> (Text, Int)
func absValue = entry =>
    mapSecond abs entry

---

mapBoth

Applies one function to the first element and another to the second.

use aivi.pair (mapBoth)

use aivi.math (
    abs
    negate
)

type (Int, Int) -> (Int, Int)
func normalizePair = pair =>
    mapBoth abs negate pair

---

fromPair

Constructs a pair from two separate values.

use aivi.pair (fromPair)

type Text -> Int -> (Text, Int)
func makeEntry = label score =>
    fromPair label score

---

toPair

Constructs a pair from two separate values. Useful as a named combinator when pairing results in a pipeline.

use aivi.pair (toPair)

type Text -> Int -> (Text, Int)
func labelScore = label score =>
    toPair label score

---

duplicate

Creates a pair where both elements are the same value.

use aivi.pair (duplicate)

type Int -> (Int, Int)
func mirror = n =>
    duplicate n

---

Compatibility aliases

fst, snd, mapFst, and mapSnd remain available for compatibility, but new code should prefer first, second, mapFirst, and mapSecond.