How to use the Emacs RPN calculator (M-x calc) in your browser

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almost Emacs calc screenshot

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A quick guide to the browser rebuild of M-x calc, the Emacs RPN stack calculator. (Background on all three “almost Emacs” tools in the original post.)

Steps

  1. Open https://www.clearevo.com/calc/ - you get the --- Emacs Calculator Mode --- buffer with a live Calc Trail pane beside it recording every operation.
  2. It’s RPN: enter numbers first, then the operator. Type a number and press RET to push it on the stack, type another, then press an operator key like + - * /.
  3. The bindings your fingers remember are there (buttons exist too):
    • RET - push / duplicate the top of stack
    • TAB - swap the top two entries
    • n - negate
    • & - 1/x
    • Q - square root
    • U - undo
    • DEL - drop the top of stack

Pure client-side, nothing leaves your machine (Google Analytics for visit stats only). If your Emacs muscle memory catches a binding behaving wrong, comment on the original post.

This tool is free software and open source: ykasidit/clearevo_online_tools - issues and pull requests welcome.

Full disclosure: this post - and any code or tool it describes - was co-authored with Claude (Anthropic’s AI, via Claude Code). I directed, guided and reviewed. I don’t want to pretend otherwise.

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