Sky.Tui overview

Status: the Rust compiler (rust/, cargo build --release -p sky) is the primary Sky compiler; the Haskell compiler is preserved under legacy-haskell-compiler/. Verified by the example sweep + compiler test suite (cargo test + xtask gates). See ../compiler/journey.md for the changelog.

Terminal-rendering TEA backend. Sky.Tui runs an init / update / view / subscriptions app the same way Sky.Live runs a web app — but the view function paints to ANSI terminal cells instead of HTML. The same Std.Ui element tree renders in both backends, so a counter, a stopwatch, or a small dashboard ports between the browser and the terminal with no view rewrites.

module Main exposing (main)

import Sky.Core.Prelude exposing (..)
import Sky.Core.Task as Task
import Sky.Core.System as System
import Std.Tui as Tui
import Std.Cmd as Cmd
import Std.Sub as Sub
import Std.Ui as Ui
import Std.Ui exposing (Element)
import Std.Ui.Background as Background
import Std.Ui.Font as Font


type alias Model = { count : Int }

type Msg = Increment | Decrement | Quit | NoOp

init : () -> ( Model, Cmd Msg )
init _ = ( { count = 0 }, Cmd.none )

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model = case msg of
    Increment -> ( { model | count = model.count + 1 }, Cmd.none )
    Decrement -> ( { model | count = model.count - 1 }, Cmd.none )
    Quit      -> ( model, Cmd.perform (System.exit 0) (\_ -> NoOp) )
    NoOp      -> ( model, Cmd.none )

view : Model -> Element Msg
view model =
    Ui.column
        [ Ui.padding 16, Ui.spacing 8 ]
        [ Ui.text ("Count: " ++ String.fromInt model.count)
        , Ui.row [ Ui.spacing 8 ]
            [ Ui.button [] { onPress = Just Decrement, label = Ui.text "−" }
            , Ui.button [] { onPress = Just Increment, label = Ui.text "+" }
            ]
        ]

subscriptions : Model -> Sub Msg
subscriptions _ = Sub.none

main =
    Tui.app
        (Tui.config
            { init = init, update = update, view = view
            , subscriptions = subscriptions
            }
        )
        |> Task.run

sky run src/Main.sky builds and launches the binary. The terminal switches to alt-screen, raw mode, and mouse tracking; teardown on exit (Ctrl-C, Quit, panic, SIGTERM) restores the user's primary screen.

Status: stable

Sky.Tui shipped as part of v0.12 and has tracked Sky.Live in the 27-example regression sweep since. The surface follows the same backwards-compatibility discipline as Sky.Live — examples/21..24 exercise the full primitive set on every release.

What works

The runtime restores the terminal in every exit path: panic, signal (SIGTERM/HUP/QUIT/INT), System.exit, normal Quit Msg. mosh sessions don't end up with a corrupted readline.

Logical-pixel canvas

Attach a logical-pixel canvas via the Tui.withCanvasWidth / Tui.withCanvasHeight builders. The runtime computes pxPerCell from the live terminal size and scales every Ui.padding 8, Ui.spacing 4, Ui.px N to character cells. Default 1280×720 matches a typical web canvas — Std.Ui apps written for the browser look right in the terminal without re-tuning. Tweak via Tui.withCanvasWidth 800 for denser layout.

main =
    Tui.app
        (Tui.config
            { init = init, update = update, view = view
            , subscriptions = subscriptions
            }
            |> Tui.withCanvasWidth 1024
            |> Tui.withCanvasHeight 768
        )
        |> Task.run

Auth guard middleware

The Tui.withGuard builder attaches a guard with the same shape as Live.app's — Msg -> Model -> Result Error (). Returning Err reason skips the update and (if your model has notification / notificationType fields) writes the rejection into them for the view to render. The same guard function works under both backends, so authentication logic stays portable.

Sky.Cli — line-oriented TEA

For apps that DON'T want raw-mode and full-screen rendering, Sky.Cli provides a line-oriented variant: the view returns a String, update consumes lines from stdin, and the runtime runs on a regular non-raw terminal. Useful for piped scripts and CI diagnostics.

Cli.readPassword : () -> Task Error String reads a line from stdin with terminal echo disabled — wraps golang.org/x/term's ReadPassword. Falls back gracefully on non-TTY stdin.

Examples

Environment variables

Reliability floor

These are enforced runtime invariants — every panic / signal / malformed input path was audited before the experimental tag.

Prior-art attribution

The TEA shape (init / update / view / subscriptions) is adapted from elm-lang's Browser.element. bubbletea's renderer inspired the safeGo + alt-screen lifecycle. See NOTICE.md.

See also

• docs/skylive/overview.md — the web-side TEA backend that shares the same Std.Ui element tree.
• docs/skyui/overview.md — the layout DSL itself.
• examples/24-tui-kitchen-sink/src/Main.sky — every supported primitive in one screen.