blog: Add 2025-07-29.md

Author: ingydotnet

blog/2025-07-27.md

@@ -1,5 +1,5 @@
 ---
-title: Fun in the FridaYS
+title: Fun in the SundaYS
 date: 2025-07-27
 draft: false
 authors: [ingydotnet]

blog/2025-07-29.md

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+---
+title: Is JSON really a subset of YAML?
+date: 2025-07-29
+draft: false
+authors: [ingydotnet]
+categories: [Summer-of-YS]
+edit: blog/2025-07-29.md
+comments: true
+---
+
+YAML is a superset of JSON.
+
+This is a basic truth about YAML.
+
+I assume that in 2025, most people who use YAML and JSON regularly already know
+this.
+
+Today I'll say a bit more about this and how it came to be.
+
+<!-- more -->
+
+
+## 2001, 2006 and 2009
+
+The fact that JSON is a subset of YAML is more of a happy accident than
+something that was planned.
+
+I started working on YAML with Clark and Oren in April 2001.
+
+We didn't become aware of JSON until 2006.
+That seemed to be the same time that almost everyone was becoming aware of JSON.
+
+I was surprised to learn much later that JSON also started in 2001!
+
+By 2006, the YAML 1.1 spec had already been published.
+
+When we took a closer look at JSON, we realized that it was basically YAML's
+flow style collections with double quoted strings.
+
+When we looked _really_ closely at JSON, we realized that there were only 3
+small issues that prevented JSON from being a subset of YAML.
+
+One of them was that the colon separator for key/value mapping pairs must have
+a space after it.
+JSON has no such requirement.
+
+We decided to take advantage of this situation and make JSON a proper subset of
+YAML for the 1.2 spec.
+
+For the colon thing we made the special rule that in a flow mapping, if the key
+is double quoted (which all JSON keys are), then the colon doesn't need
+whitespace after it.
+
+I forget the other two issues.
+It was a while ago!
+
+That came out in 2009.
+
+
+## But is JSON really 100% a subset of YAML?
+
+As far as we (the current core YAML dev team) know, yes, JSON is really 100% a
+subset of YAML.
+
+This has been challenged from time to time.
+
+Each time that it is challenged, we have to go back and look at the spec closely
+and check.
+So far we have fallen on the happy YAML side.
+
+It's entirely possible that there is a corner case that we have missed.
+
+IF someone finds one, I guess we'll have to put out a new YAML 1.3 spec.
+
+
+## The importance of JSON, YAML and YS
+
+JSON is a very simple and trustworthy format.
+
+It's hard to mess it up.
+
+It's super reliable for data that you don't have to look at or maintain.
+
+YAML is better for that.
+
+Since JSON is a subset of YAML, you can easily write and maintain data in YAML
+and then convert it to JSON for the machine.
+
+JSON plays an important role for YS too.
+
+YS considers JSON to be the Lingua Franca of data.
+
+When you load a file with YS, the return value is always a data structure
+of the JSON data model.
+
+In fact, a libys.so binding library for any given programming language currently
+has one function:
+
+The `load` function takes a YS/YAML/JSON string and returns a JSON string that
+is then decoded by the library into a native data structure for that language.