one type for emptiable and safe non-empty

emptiness typed

🧩 Read about allowable state first

📦 Emptiable ..... Never | Possibly

A Maybe value that can be made non-empty depending on what we know – an "emptiable-able" value

import Emptiable exposing (Emptiable, filled, fill)

type alias TextFilled =
    { first : Char, afterFirst : String }

first : Emptiable TextFilled Never -> Char
first =
    fill >> .first

maybeFirst :
    Emptiable TextFilled possiblyOrNever
    -> Emptiable Char possiblyOrNever
maybeFirst =
    Emptiable.map (filled >> first)

📚 Stack

Handle lists that are Possibly or Never Emptiable in one go

Emptiable ... Never allows safe Maybe-free top, removeTop, fold (for finding the maximum etc.; some call it "fold1"), ...

That's more useful than you might think.

import Linear exposing (Direction(..))
import Emptiable exposing (Emptiable)
import Stack exposing (Stacked)

Emptiable.empty
    --: Emptiable (Stacked element_) Possibly
    |> Stack.onTopLay 0
    --: Emptiable (Stacked number_) never_
    |> Stack.attach Down (Stack.topBelow 1 [ 2, 3 ])
    --: Emptiable (Stacked number_) never_
    |> Stack.toTopBelow
--> ( 1, [ 2, 3, 0 ] )

where emptiness-typed is already being used

• 🗃️ elm-keysSet
• 📜 elm-scroll
• 🚥 typesafe-array

suggestions?

→ See contributing.md