The type of fully constructed KeysBeingBuilt ready to use.

"infer types" is your friend here

import Keys exposing (Keys, Key)
import Order
import Char.Order
import String.Order
import Emptiable
import N exposing (Up, To, N0, N1, N2)


userKeys :
    -- just infer this
    Keys
        User
        { name :
            Key
                User
                (Order.By
                    User.Name
                    (String.Order.Earlier (Char.Order.Alphabetically Order.Tie))
                )
                String
                (Up N1 To N1)
        , email : Key User (Order.By User.Email Email.DefaultOrder) String (Up N0 To N1)
        }
        N2
userKeys =
    Keys.for (\name email -> { name = name, email = email } )
        |> Keys.by ( .name, User.name )
            (String.Order.earlier (Char.Order.alphabetically Order.tie))
        |> Keys.by ( .email, User.email )
            Email.defaultOrder


Emptiable.empty
    |> KeysSet.insert userKeys
        { username = "ben", email = [email protected].. }
    |> KeysSet.insert userKeys
        { username = "mai", email = [email protected].. }
    -- not inserted
    -- There's already an element where .email is [email protected]..

What's with those Up N.. To N..? Internally, each key will be assigned an index. that type from bounded-nat preserves the knowledge that each key's index is less than the whole count.

Tags correctly constructed Keys (and each Key)

By which aspect = key and in which key Order elements should be sorted

Ordering by the element itself.

Short for

Keys.identity order =
    for identity |> by ( identity, Map.identity ) order

in KeysSet

import Map
import Order
import Int.Order
import N exposing (Up, To, N0)
import KeysSet


intIncreasing : Keys.Identity Int Int.Order.Increasing
intIncreasing =
    Keys.identity Int.Order.increasing


KeysSet.fromList intIncreasing [ -1, 5, 5, 8, 7 ]
    |> KeysSet.toList ( intIncreasing, Basics.identity )
--> [ -1, 5, 7, 8 ]

Resulting type of Keys.identity.

import Map
import Order
import Float.Order
import N exposing (Up, To, N0)
import KeysSet


floatIncreasing : Keys.Identity Float Float.Order.Increasing
floatIncreasing =
    Keys.identity Float.Order.increasing


KeysSet.fromList floatIncreasing [ -1.1, 5, 5, 8.7, 7.8 ]
    |> KeysSet.toList ( floatIncreasing, Basics.identity )
--> [ -1.1, 5, 7.8, 8.7 ]

Start a keys builder by giving names to the individual keys as arguments using a record

userKeys :
    Keys
        User
        { email : Key User (Order.By User.Email Email.Order) Email (Up N0 To N0) }
        N1
userKeys =
    Keys.for (\email -> { email = email })
        |> Keys.by ( .email, User.email, Email.order )


Emptiable.empty
    |> KeysSet.insert userKeys
        { name = "ben", email = "[email protected]" }
    |> KeysSet.insert userKeys
        { name = "mai", email = "[email protected]" }
    -- not inserted
    -- There's already an element where .email is "[email protected]"

Once you supply all the necessary key-Orderings with by, a KeysBeingBuilt is automatically of type Keys.

So if you for example infer the type

KeysBeingBuilt element { yourKeys } { yourKeys } keyCount

you can replace it by

Keys element { yourKeys } keyCount

It's data is unaccessible because you shouldn't be able to

• retrieve it's keys to use in different Keys
• have an out of sync array representation

Add a key

• what name does the key have? (same as in the initial record from Keys.for)
• which aspect should be sorted by? → Mapping
• how should we compare these aspects? Ordering

List all keys in the keys record as an array of functions determining the Order of 2 elements

How to turn the element into the specified key

How to order by the specified key

A Key's distance from the first by in the Keys builder