Rio

Text editor & development environment

Back to the future.

A lightweight IDE in the spirit of ’90s desktop software.

adr/0004-tcl-tk-and-ck.mdRaw Markdown · GitHub ↗

ADR-0004: Tcl/Tk for core and GUI, Ck for the TUI

  • Status: Accepted; the TUI is deferred by ADR-0112
  • Date: 2026-06-24
  • Deciders: jka
  • Decision: D4

Context

rio needs to run on Linux (Debian, Alpine), the BSDs and Windows, with a graphical and a terminal face. The maintainer wanted a from-scratch project in Tcl/Tk, and the implementation language decides how much of the frontend code the two faces can share.

Decision

  • The core and the GUI are written in Tcl/Tk. Tcl/Tk has real cross-platform reach, single-file distribution options (Tclkit, starpacks, vanillawish), and a strong editing widget.
  • The TUI uses Ck, a Tk-shaped toolkit that renders to curses with Tk-parallel widgets (text, listbox, entry, frame, menu, scrollbar) and the same geometry managers. Candidate builds are vzvca/ck8.6 and vanillatclsh.
  • rio is Tcl throughout. No other implementation language is used in the project, including for scratch scripts or build helpers.

The contributor toolchain is tcl, tk, tcllib (for json), tcl-tls and git. install-unix.sh installs it on apt, apk and pkg_add systems and can build Ck from source.

Alternatives considered

  • Writing a TUI toolkit from scratch. Rejected: Ck provides Tk-parallel widgets and removes the riskiest custom work.
  • Perl/Tk with Curses::UI. Perl has a more mature TUI library, but the same dated Tk and a weaker single-binary story. Kept only as a fallback if Ck failed.

Consequences

  • The GUI and a future TUI can share idioms, not only the core.
  • Headless Tcl must not load Tk (see ADR-0001).
  • The Ck spike (ADR-0112) passed on rendering and layout and found cross-terminal keyboard handling to be the real cost; the TUI was then deferred.