Xah Talk Show 2026-01-21 Ep748 emacs lisp, write command to eval selection, fsharp, JavaScript.

• https://youtu.be/v927pcyYI10

Video Summary (Generated by AI, Edited by Human.)

Write an Emacs Lisp command to evaluate selected regions of code, specifically for fsharp.

• Demo JavaScript Eval Region (0:52).
• Intro the Problem: fsharp Eval Region (4:19)
• Code Copying and Modification (5:37). involves changing the command name and identifying necessary adjustments for fsharp.

• learning dotnet fsi (6:40): how to execute fsharp scripts, specifically using the dotnet fsi command.
• The challenge lies in passing fsharp expressions as standard input rather than as files.

• Exploring Command Line Options and Documentation (10:00): look into the help documentation for the dotnet command, discussing the complexities of command-line arguments, especially when dealing with various programming languages and their execution environments.
• Discussion on File vs. Standard Input (17:08): A detailed explanation is provided about the benefits of piping code to standard input versus writing to and reading from temporary files, emphasizing performance and avoiding file management overhead.
• Seeking AI Assistance (30:19): The presenter uses an AI tool to inquire about how dotnet fsi accepts fsharp expressions from standard input, confirming that piping directly to it is the intended method.
• Testing and Initial Results (36:15): The newly modified fsharp evaluation command is tested.
• While it successfully executes the fsharp code, it also outputs extraneous copyright and interactive shell information, which needs to be addressed.
• Acknowledging Remaining Issues and Future Steps (37:54): The video concludes with the presenter acknowledging that the output needs to be refined and that further investigation into the dotnet fsi command-line options is required to suppress the unwanted output.
• The presenter also shares the Emacs Lisp code developed during the show.

• Emacs: Xah Fly Keys 📦

• Ultimate Hacking Keyboard 80 (UHK 80)
• Nulea M505 Trackball
• Huion H640P Drawing Tablet

• Fsharp Learning Notes

• JavaScript in Depth

• the job is to write a xah-fsharp-eval-region
• we already have xah-js-eval-region

• how to get dotnet fsi to accept a fsharp expression from stdin
• answer: just pipe to dotnet fsi --quiet

console.log( 3 + 4 )

let x = 3
printfn "%i" (x+4)

printfn "%i" (3+4 )

(defun xah-fsharp-eval-region (Begin End &optional zinsert-output zadd-print)
  "Eval the current region in dotnet fsi, print result in buffer *xah fsharp output*.
If there is no text selection, eval current text block.

If `universal-argument' is called first, insert result below the region.

Require the external command dotnet.

Created: 2026-01-21
Version: 2026-01-21"
  (interactive
   (let (xbeg xend)
     (if (region-active-p)
         (setq xbeg (region-beginning) xend (region-end))
       (let ((xp (point)))
         (save-excursion
           (setq xbeg (if (re-search-backward "\n[ \t]*\n" nil 1)
                          (match-end 0)
                        (point)))
           (goto-char xp)
           (setq xend (if (re-search-forward "\n[ \t]*\n" nil 1)
                          (match-beginning 0)
                        (point))))))
     (list xbeg xend current-prefix-arg)))
  (let ((xoutbuf (get-buffer-create "*xah fsharp output*")))
    (with-current-buffer xoutbuf (erase-buffer))
    (call-process-region Begin End "dotnet" nil xoutbuf t "fsi" "--quiet")
    (if zinsert-output
        (progn
          (goto-char End)
          (insert "\n")
          (insert-buffer-substring xoutbuf))
      (progn
        (display-buffer xoutbuf)))))