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YS for Clojurians

If you happen to already be fluent in the Clojure programming language, you have a huge head start for learning YS; at least for reading and understanding YS code.

For the most part understanding YS code is a matter is simply understanding a bunch of simple transformations that turn it into Clojure code.

This page will cover most of the transformations you'll need to know.

Note

After reading this page, you should be able to read YS code and also be able write working YS code fairly easily. To write really good, idiomatic YS code, you should also be well versed in all the various YAML forms, and when to best use them. Like anything, practice makes perfect!

Foreword🔗

YS is a language made from a combination of YAML and Clojure, and its design tries to combine the best of both worlds. This might seem like a bad idea at first, but it actually works out surprisingly well.

YS interpreter (compiler and runtime) is:

  • Written in Clojure
  • Compiles to Clojure code
  • Evaluates with a Clojure runtime

But the primary YS audience is not Clojure programmers! While YS is a complete programming language, and can be used for any task in general, it will likely be most useful for people who need more from their YAML. All YAML config files are valid YS code and YS code is always 100% valid YAML.

This document is not an attempt to convert Clojure programmers to YS. It is simply meant to help people learn YS faster if they already know Clojure.

Syntax Intro🔗

Clojure is a Lisp. Lisp code is comprised of list forms, value forms, comments and whitespace. Clojure has a somewhat richer syntax than your typical Lisp, adding brackets and braces for some forms and reader macros for others. Still, structurally there is very little to learn.

YAML code is a data language that unlike JSON or EDN offers quite a few syntactic constructs like comments, anchors, aliases, tags, block (indented) and flow (bracketed) collections styles and 5 different scalar quoting styles: plain (unquoted), single quoted, double quoted, literal and folded.

YS makes use of all of these constructs to make a clean looking programming language that simultaneously works as a data language.

The main takeaway here is that YS offers a lot more flexibility in ways to write code than Clojure (Lisp) does.

Note

Whether "more" ways is better or worse is entirely up to you. It's just important to point out from the start that YS has this flexibility and you should expect to see it in the code.