Tuple.md

Module Elm.Tuple

Some helpers for working with 2-tuples.

Note: For larger chunks of data, it is best to switch to using records. So instead of representing a 3D point as (3,4,5) and wondering why there are no helper functions, represent it as { x = 3, y = 4, z = 5 } and use all the built-in syntax for records.

This module was added in Elm 0.18.

Implemented using Purescript's Data.Tuple

first

first :: forall a1 a2. Tuple a1 a2 -> a1

Extract the first value from a tuple.

first (Tuple 3 4) == 3
first (Tuple "john" "doe") == "john"

Equivalent to Purescript's fst

second

second :: forall a1 a2. Tuple a1 a2 -> a2

Extract the second value from a tuple.

second (Tuple 3 4) == 4 second (Tuple "john" "doe") == "doe"

Equivalent to Purescript's snd

mapFirst

mapFirst :: forall a b a2. (a -> b) -> Tuple a a2 -> Tuple b a2

Transform the first value in a tuple.

import String

mapFirst String.reverse (Tuple "stressed" 16) == (Tuple "desserts" 16)
mapFirst String.length  (Tuple "stressed" 16) == (Tuple 8 16)

Equivalent to Purescript's lmap

mapSecond

mapSecond :: forall a b a1. (a -> b) -> Tuple a1 a -> Tuple a1 b

Transform the second value in a tuple.

import String

mapSecond sqrt          ("stressed", 16) == ("stressed", 4)
mapSecond (\x -> x + 1) ("stressed", 16) == ("stressed", 17)

Equivalent to Purescript's map