I understand your frustration, but I just have to ask the question:

What modern language has native support for JSON?

• JavaScript has JSON.parse & JSON.stringify to decode & encode JSON via the std library

• Python has json.loads & json.dumps to decode & encode JSON via import json

• PHP has json_decode & json_encode to decode & encode JSON via the std library

• Ruby has JSON.parse & JSON.generate to decode & encode JSON via require 'json'

• … [1]

The point I’m trying to make is that there doesn’t appear to be a modern language that has – what I would be willing to call – native support for JSON.

Every widely used (modern?) language has functions or methods to encode & decode its native objects or data structures to/from JSON.

Even JavaScript (the ‘J’ in JSON) doesn’t appear to have native support.

JSON (JavaScript Object Notation) is a lightweight data-interchange format [1], and in being such, I believe every language would need to attempt to parse JSON order to determine whether it’s valid or not, and Elixir is no exception.

1. json.org

Guard clauses map to VM level instructions, you can only use those specific clauses in guards, in combinations. The only way to know that a string is JSON is to parse it, and I don’t see how you could create a set of guard clauses that would parse JSON.

That is not true. Few aren’t constant time:

• length/1 is linear
• is_map_key/2 and map access (map_get/2) are logarithmic (and dependants like is_struct/{1,2}

Yes, lists are singly linked lists and must be iterated to the end to find out the length. That’s why list == [] is recommended over length(list) == 0.

Use Jason.decode! to throw or Jason.decode and pattern match on the result. Not in a guard though.

Or similar in whatever json library you’re using.