What's new

What each release of Tessel brought, newest first. To get the latest, run tessel update (or take the update the IDE offers). See Installation if you don’t have Tessel yet.

Tessel’s first releases came quickly, several on some days, so each day’s are listed together under its last version. See How Tessel is made.

0.1.43

October 10, 2026 · 0.1.42 and 0.1.43

Apps for Android. tessel build --android makes an app an Android package from the same code: an .apk to install on a phone, or with --bundle an .aab for Google Play, signed with your own key. On a phone, a finger taps and scrolls, a long press opens context menus, the app stays clear of the system’s bars and the on-screen keyboard, follows the dark theme, and Back closes what’s on top. tessel android doctor checks that Android’s tools are installed. This is a first version: text input is basic, and system dialogs aren’t there yet. See Building for Android.
async and await. Steps that wait for something (a download, a timer, work in the background) can be written one after another, where they used to nest in blocks: let text = await fetch(url: address). await works on every function that ends with a completion block, so fetch, after, request, download, runCommand, background and your own such functions can be awaited as they are. Functions that wait are declared with async fn, and a button’s action (or any block that gives no value) can await directly. See Waiting with async and await.
Constants. A let at the top of a file is a constant the whole program can use: let maxPlayers = 4. See Constants.
Computed properties. area: Float { width * height } in a struct or enum is read like a field, rect.area, and worked out each time. See Computed properties.
Static members. static let and static fn belong to a type and are used through its name: Rect.zero, Rect.square(side: 2). See Static members.
async, await and static are only keywords where they’re used this way, so programs that use them as names still build.

0.1.41

October 8, 2026 · 0.1.40 and 0.1.41

Smaller apps and faster builds for programs with large structs. A struct of more than about 16 fields is now moved as one block of memory, where each use of it used to cost code for every field. An app of 98,000 lines built around one large struct went from 73 MB of code and 12 minutes to build, to 13.6 MB and under a minute. Smaller structs are as before.
A function kept in a struct’s field is called like a method: rule.applies(4). See Function types.
Fixed:
- A struct with a field holding a function crashed the compiler when it was passed to a bind parameter.
- Escape didn’t close a popover (or a sheet) in an app with .onKeyEvent: the app got the key.
tessel --version says which version a project uses, when the project is pinned to another one than is installed: tessel 0.1.36 (this project uses 0.1.38).
Fixed: an index that’s a call changing the list it indexes, through a bind parameter (list[grow(list)]), read the list as it was before the call, and could stop the program.

0.1.39

October 7, 2026 · 0.1.38 and 0.1.39

Dialogs. alert and confirm show the system’s message dialogs, chooseFolder asks for a folder, and openFiles for several files. See Dialogs and sheets.
Sheets. .sheet(isPresented:) shows your own views in a card over the dimmed window, and dismiss() closes it. TextPrompt asks for a text and ProgressPanel shows work going on, ready-made for a sheet. See Sheets.
Pickers: DatePicker and Calendar for dates, TimePicker for the hour and minute, and FontPicker for a font family. See DatePicker.
Notices: showNotice("Saved") shows a short message that goes by itself. ProgressBar shows how far something is.
Printing: printDocument draws pages as writePDF does and prints them: through the system’s print dialog on macOS, and the PDF app on Windows. See Printing.
Ribbons in several files. A view of your own can make a ribbon’s tab, a group, or some of a group’s buttons, and the ribbon uses them as if they were written in it. See A ribbon in several files.
Fixed:
- g.textWidth left out the spaces at the end of a text, so a space alone was 0 wide.
- Padding on a Divider made the line thicker instead of leaving room around it.

0.1.37

October 6, 2026 · 0.1.36 and 0.1.37

tessel new starts a project from a template: a small to-do list app in a few files (the default), an app with one window, or a command-line program, with a tessel.toml, a README and a .gitignore. The IDE offers the same templates in an empty folder. See tessel new.
Databases. openDatabase opens (or creates) an SQLite database file, and execute and query run SQL on it, with values filled in for ?s. SQLite is built into Tessel, so it works the same on macOS and Windows with nothing to install. See Saving data in a database.
Font families and italic. .font(italic:family:), and the same on g.text and g.textWidth: any installed font by name, or "monospaced". A font that isn’t installed falls back to the system’s. fontFamilies() lists the fonts installed. See font.
Password fields: TextField(secure: true) shows a dot for each character, and its text can’t be copied. See TextField.
Hashes: data.hash() gives SHA-256, SHA-1, SHA-512, MD5 and other digests, and data.hex shows bytes as hexadecimal. See hash and hex.
wrappingAdd, wrappingSubtract and wrappingMultiply on Int, for hashes and checksums written in Tessel.
Fixed: == between two cases of an enum whose cases hold different values crashed.

0.1.35

October 5, 2026

Ribbons. Ribbon, RibbonTab and RibbonGroup lay out tabs of grouped commands, as office apps have, with large and small buttons, toggles and menus (RibbonButton, RibbonToggle, RibbonMenu). Groups shrink to fit a narrow window. See Ribbons.
48 more built-in icons, for ribbons and toolbars: cut, paste, bold, the alignments, charts, sort, filter, sum and more. See Icons.
The app’s manifest. The [app] table of tessel.toml gives the app’s name, identifier, version, author, copyright, icon, category and the files it opens. App bundles on macOS and .exe files on Windows carry them, the About panel shows them, and appInfo() gives them to the program. See The project file.
text += more is fast: it adds to the string where it is, as += on a list does (200 000 appends: 7 ms instead of 6 s).
Fixed:
- toJson on a type that contains itself (an enum of lists of itself, a tree) crashed the compiler.
- Menu bar shortcuts didn’t run in a view with .onKeyEvent.
- saveFile with several types added a second extension.
- In test scripts, key shift+5 types %, and type with no field edited presses each key.

0.1.34

October 4, 2026 · 0.1.30 to 0.1.34

PDF documents. writePDF draws pages with the same Graphics as a Canvas, and g.newPage() starts the next one. Text stays text that can be selected and searched, with its fonts in the file; shapes stay sharp at any zoom. See Making a PDF and writePDF.
Much smaller apps on Windows. Apps draw, lay out text and read pictures with what comes with Windows (Direct2D, DirectWrite and WIC), as they do on macOS: a one-Text app is about 1.3 MB instead of 7.5 MB. See How big an app is.
A project chooses its version of Tessel. tessel pin writes the version into the project’s tessel.toml, and from then on Tessel’s commands, editors and the IDE use that version for the project, installing it the first time. See tessel pin.
Functions can change the caller’s value. A parameter declared bind is the caller’s variable, field or list item itself, not a copy, as it already was for views: fn addBonus(scores: bind [Int]). Methods can have them too. See Changing the caller’s value.
New controls: Slider, Stepper, ColorPicker, DisclosureGroup (for trees) and LazyVStack (for long lists). See Controls.
Drag and drop between views with .draggable and .dropTarget, and every key with .onKeyEvent. Keyboard shortcuts can ask for Shift and Alt: .shortcut("shift+z").
Background jobs report their progress and can be cancelled.
Drawing: pictures made from pixels, gradients, layers that blend with what’s under them (on Windows too), and SVGs on a Canvas. See Drawing.
Menus and windows: context menus, popovers, the menu bar (the system’s on macOS), more than one window, asking before a window closes, and files opened with the app. See Menus, windows and documents.
Language: bit operations, hex and binary number literals, match arms with several patterns, tuples in if let, and functions declared inside functions. Data can have bytes appended to it. See Basics and Functions.
Fixed:
- Changing a loop’s variable through a closure (or a bind argument) changed a copy of the list, not the list.
- Appending many bytes to a Data could damage it.

0.1.29

October 3, 2026 · 0.1.23 to 0.1.29

Much smaller apps. On macOS, apps draw, lay out text and read pictures with what comes with macOS, so a one-Text app is about 1 MB instead of 8.3 MB. Apps carry SVG, pictures and Markdown only when they use them, and Windows apps no longer carry all of Tessel (a one-Text app was 24 MB). See How big an app is.
IDE: the Design panel has an inspector, undo and redo, copy, cut, paste and duplicate, an outline of the views, and more views to add (TextField, Toggle, Picker). A Preview panel shows Markdown files as they’ll look, next to their text. See The Design panel.
A code editor’s undo history includes the changes the program makes to its text. New: undoTextEdit() and redoTextEdit().
A click inside a view with .onKey gives it the keyboard.
tessel preview --dark.
Fixed:
- On Windows, the REPL, hot reload and previews could crash, and endless recursion ended the program instead of being reported as a Tessel error, as on macOS.
- pow(10, x) failed to build on macOS.

0.1.22

October 2, 2026 · 0.1.14 to 0.1.22

IDE: the Design panel. A picture of your app next to its code, where views can be selected, changed, added, moved and deleted. Every change is written into the code. See The Design panel.
Canvas: draw views of your own with paths, shapes, text and pictures, and save drawings as pictures. See Drawing and the mouse.
The mouse and keys: .onPointer, .onKey, .onDrag, .cursor, .onDrop, .onResize, .tooltip, .offset and .clipped.
A Markdown view: text with headings, lists, code, tables, pictures and links.
Scroll bars in scroll views and code editors, which show when there’s more than fits and can be dragged.
IDE: the documentation comes with it: the Docs button opens it next to the editor, without a network, with search. The explorer, the bottom panel and the Docs panel can be resized by dragging their edges.
tessel preview makes a picture of an app’s window for editors. See tessel preview.
Data reads numbers, slices and Latin-1 text, and compresses. list += other appends in place. readImage gives a picture file’s size and pixels, and appendData adds bytes to the end of a file.
CodeEditor: taller lines, and more room around the line numbers and the code.
Releases are for macOS and Windows together from now on.
Fixed:
- Stopping tessel run left the program it started running.
- A double click in a code editor or text field could select only part of a word.

0.1.13

October 1, 2026 · 0.1.8 to 0.1.13

tessel repl: type code and see what it does, a line at a time. An import stays for the rest of the session, so a project’s modules can be tried out at the prompt. See The REPL.
Hot reload: tessel run --hot gives a running app its new code when you save, and keeps its state. In the IDE, “Reload on save”.
Light and dark: apps follow the system, or choose one with app Name(appearance: .dark). Colors of your own with .rgb and .rgba.
.animation(): views move, resize and fade to their new state.
Image shows PNG and JPEG files.
Tab and Shift+Tab move between text fields, and input methods (Chinese, Japanese, Korean, accents) work in them.
Time zones for date, formatDate and parseDate, and calendar dates: dateParts, addToDate, daysBetween and more.
cancelRequest gives up a request or download. WebSockets can send and receive bytes.
print shows lists, dictionaries, sets and tuples. enumerated(), zip, and for (key, value) in dictionary.
Code completion in any editor through tessel lsp. See Editor support.
App icons: an icon.png next to a program is its app’s icon.
Fixed: REPL errors point at the right column, and every entry has its own number.

0.1.7

September 30, 2026

Tuples and sets. See Collections.
Modules: import geometry, with public and private. See Programs and files.

0.1.6

September 29, 2026

Errors with reasons: Result<T>, Error and try. See Errors.
Clearer error messages for beginners, and a 21-lesson course for learning to program with Tessel.

0.1.5

September 28, 2026 · 0.1.4 and 0.1.5

Interfaces. See Interfaces.
Generics: generic functions, structs and enums, with interface constraints. See Generics.
while, while let, break and continue, and reading input from the command line.
Faster lists, dictionaries, math and text.

0.1.3

September 27, 2026 · 0.1.0 to 0.1.3

The first release: the language, the UI toolkit, the compiler, and the IDE.
A much larger standard library: text, lists, numbers, math, dates, files, the clipboard, and the network (requests, downloads, WebSockets). JSON and binary saving. Work on another thread with background.
Open and Save dialogs, and number formatting with formatted(decimals:).
tessel update, and updates offered in the IDE. Code completion in the IDE, which offers to create main.tsl in an empty folder.
Apps about a third smaller.
Fixed: four compiler crashes and several wrong results. Callbacks (timers, requests) work in fn main programs, and .hoverBackground works on any view.