Cypress, React and Emacs backup/lock files

 So I'm dealing with some javascript lately, and it took me a while to figure out that some of the javascript tooling ("cypress open", or "yarn start" a react app) fails to refresh correctly (in fact exits with an exception) every time you modify a file that it is watching.

So, if autorefresh is "on", you can't touch any file.  Not good.

Found out that the cause of those failures are both emacs lockfiles and backup files. They are created in the source directories, and then, js tries to load them, or to examine them somehow, and js falls flat on its face.

(setq make-backup-files nil  

         create-lockfiles nil)  

That should do it.

Disable towardsdatascience and hbr paywall

...By autopopping an incognito window ...

N Good Javascript Tutorials

There's so much about javascript on the web that it's always been hard (for me) to find good resources.  But I think I found these N tutorials that are pretty good.

• https://javascript.info/
• https://exploringjs.com/deep-js/
• https://stjs.tech/
  
• https://js4ds.org/
  

Good tutorials are hard to find and keeping the good links is important. I'm keeping also this docker tutorial. I just wish I've had it 3 years ago.

MemoYzing: memoize using Y Combinator

Lately I've had to speed up an openresty-lua application.  As most of the code is just applications of transformations to data, and it's mainly functional, I thought that memoizing would be the easiest way to go.

After generating a flamegraph for the code, I spotted a couple of functions that could be memoized. Problem solved.

While looking for a nice way to write the memoize function, I remembered the shortest memoizing code ever in lua. Also I googled a bit and found kikito's memoize library. So far so good. But they both share a problem. What about recursive functions? They will get catched only on the top level, because the self referencing calls , after memoizing are not self referencing anymore, and they point to the old function.

Perl memoize module overwrites the symbol table to alias the functions. In ruby 2.0 you can memoize a recursive function using Module#prepend. With the Y combinator

Here's this article from Matt Might about how YCombinator makes it possible to turn a recursive function into a memoized recursive function caching the intermediate results, using the indirect self-reference that it provides.


EDIT: I just published the button and then thought "what if I wanna convert a doubly  recursive function (fib) into a iterative one (tail call) by using accumulators? I can obviously memoize according to the two args, but it gets pretty useless, as the results can be hardly reused. I found this series of articles "from recursion to iteration" that provide some tricks. Haven't fully understood it, but I'm on it.

Learn javascript as a little schemer

I recently found a blogpost talking about javascript prototypes in a very funny and uncommon way. It was funny to read, easy to follow, and high on insights. Out of the sudden, something clicked in my brain, and I thought:

 - Aha!, I've seen this way of explaining things in some other place! It's like the Little Schemer (and all the schemers collection (which I haven't read (yet)))!

 Then, I checked other posts on the same blog, and most articles follow the same socratic experience of explaining things.

 Really, it's funny, and it builds up on you.

 Well, and here's the url of the blog. Kudos to AngusCroll (author), you have a new blog follower.


EDIT: I just found another instersting post for js wannabies like me. Simpler, but interesting read

functional javascript

I already wrote one post some time ago about some javascript that enabled more confortable functional style programming.

Now I come with a few more (that mostly bring bundled functional capabilities in a single package)

Here's a library that brings map,filter,reduce,currying, and some inline string->function->evaluate automatisms.

http://osteele.com/archives/2007/07/functional-javascript

And a more DIY text with quite a few nice tricks.

http://seanhess.github.com/2012/02/20/functional_javascript.html