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The Axis of Eval

Manuel Simoni's blog about programming (languages).

Thursday, May 2, 2024

Delimited Generators - A more natural API for JS generators

I have been studying ways to work around the [S:horrors:S] issues of
JavaScript's async APIs for years. I have even built a series of
increasingly elaborate continuation-based Lisp interpreters (here's
the latest one, it's quite good, if I may say so).

But recently I finally came to the point where I understood JS
generators well enough to realize that generators already solve the
problem! With a small constant syntactic overhead (having to use 
function* to define generators, having to use yield* to call them,
and using next() to call them from non-generator functions), one can
program asynchronous code in a quasi-direct style.

But the plain generator interface is rather low-level, and not very
intuitive to use. So I built delimgen, a thin layer on top of plain
generators, that mimics delimited control. Delimited control is
initially hard to understand, but once you grok it it's a very
natural approach (previous post).

Here's how a simple delimited generator looks like. See it in action
here.

You can easily spawn multiple independent generators. See it in
action here.

You can also do blocking event loops easily. See it in action here.

I'm not claiming any novelty here. You also cannot do anything with
this library that you couldn't do with plain generators, but for me,
seeing that you can write quasi-blocking code in JS with some small
overhead was a real eye opener.

Update: Thanks to mmastrac on HN for pointing out that this leaks
stack - back to the drawing board!

(also: Lobsters, with an alternative formulation using async/await by
easrng)
Posted by Manuel Simoni at 11:23 #

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