Feather – a fresh Tcl reimplementation (WASM, Go)
Hey HN! First time showing something here, but I've been furiously working over the holidays on Feather, a from scratch reimplementation of TCL designed for embedding in modern applications. It's starting out as a faithful reimplementation of TCL without I/O, OOP features, or coroutines. TCL has a special place in my heart because the syntax is so elegant for interactive use, and defining domain specific languages. My motiviation is twofold: faster feedback loops for AI, and moldable software for users. It turns out giving AI agents access to the runtime state of your program makes for…
In plain words
Feather is a from-scratch reimplementation of Tcl designed for embedding in modern applications, available as WebAssembly and Go versions. It provides Tcl's elegant syntax for interactive use and domain-specific languages without I/O, object-oriented, or coroutine features. Built to enable faster feedback loops for AI agents accessing program runtime state and to support moldable software experiences, Feather avoids the complications of embedding traditional Tcl with its bundled event loop and GUI framework.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Hey HN! First time showing something here, but I've been furiously working over the holidays on Feather, a from scratch reimplementation of TCL designed for embedding in modern applications. It's starting out as a faithful reimplementation of TCL without I/O, OOP features, or coroutines. TCL has a special place in my heart because the syntax is so elegant for interactive use, and defining domain specific languages. My motiviation is twofold: faster feedback loops for AI, and moldable software for users. It turns out giving AI agents access to the runtime state of your program makes for really fast feedback loops, but embedding existing options in a world where shipping binaries for each platform is commonplace is tricky. Embedding the real TCL is tricky because it comes with its own event loop (in 2025 you alreay have one), a GUI framework (you have a web framework already, or develop on mobile), and has access to the filesystem (don't forget to delete all commands with file system access!). Feather just doesn't ship with those - expose only what you need from your application. A WASM build comes out of the box and clocks in at ~120kb plus 70kb for connecting it to the browser or node.js. And if embedding becomes easy, you can put a REPL everywhere: in mobile apps, in desktop software, as a control plane into web servers. I want to imagine a world where all software is scriptable just like Emacs and nvim, with agents doing the actual work.
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