Where parallels cross

Interesting bits of life

Moldable Emacs: mold can now update themselves with their :when clause!

Too long; didn't read

I added a mechanism to refresh mold buffers contents: define a :when clause for the mold looking like (:when (:fn 't) and the mold content will reload periodically.

The problem

Molds take a buffer (or parts of it) and transform its information into a new buffer. The manipulated data remains in the output buffer as local variables (self and mold-data). That is important because now you can develop your data exploration as a cascade of transformations. Indeed molds are also compo sable.

Now, what happens if the original buffer on which you applied a mold changed? So far, a user would need to apply the mold again. That worked for me until now: I started using the "OrgTablesToDotPicture" mold more seriously and this repetition started troubling me.

That mold transforms Org Tables with the right schema to a Graphviz picture. That means that each time I was changing my Org Tables I had to re-run my mold. I needed a faster feedback loop to produce my graphs! And many more molds would became amazing with an updating mechanism.

How can we make this update automatic?

And there is a solution

An idle timer! Actually we need a predicate to know when to update. If the predicate is true and we are in the right context (i.e, we see the original and the result buffer of the mold), we want to update the resulting buffer.

Let me give you a sense of this with my "OrgTablesToDotPicture" mold.

This is just very useful to me. I can see how my tables look as a graph AND I can access their data as Elisp. (I can even generate these tables via Elisp but that is a story for later)

This particular mold is a composite one: it calls two molds in sequence (i.e., "OrgTablesToDot" and "DotToPicture").

The :when predicate looks like this:

:when (:fn
         (ignore-errors (unless (s-contains-p "| key" (thing-at-point 'line)) (goto-char (search-backward "| key"))))
          (equal (ignore-errors me-org-tables-to-dot) ;first time this is undefined
                 (setq-local me-org-tables-to-dot (me-all-flat-org-tables))))))

It searches the first Org Table with the right schema (very hacky!) and checks if the table data has changed from last time.

This is the only mold with such a condition for now. Still this is very exciting for me. I have been thinking about a mold that can explain errors from a while (I mean if a regexp appears in the buffer, the mold should explain what it is about from a note you have somewhere) and I feel this could make it super useful.


Auto-update your molds and make your feedback loop short! Define the :when clause and let moldable-emacs do the heavy load for you.

Happy refreshing!