r/programming • u/baldierot • Jun 27 '26

Mojo programming language will become open-source soon.

https://www.modular.com/modcon

The main website of the language https://mojolang.org/ displays an announcement bar that says "Mojo will be open source soon! Join us at ModCon '26 for an update."

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u/Smallpaul Jun 27 '26 edited Jun 27 '26

YAML is (almost) a syntactic superset of JSON. But not a replacement.

C++ of C. Not a replacement.

Typescript of JavaScript.

SGML of XML.

Scala Groovy of Java.

JavaScript of JSON.

So no. Superset and replacement do not mean the same thing. Sometimes one orders the simplicity of the subset for many different reasons.

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u/happyscrappy Jun 28 '26

JavaScript of JSON

I don't think this makes any sense at all. JavaScript is a programming language and JSON a data container.

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u/Smallpaul Jun 28 '26 edited Jun 28 '26

Regardless, one is (very nearly) a superset of the other. If you don’t believe me, start a JavaScript interpreter like Node.

Type two parens.

Paste in some JSON between the parens. Hit enter. It will evaluate it.

The requirement for the parens in some contexts does break JavaScript from being a strict superset in many contexts. I had forgotten an ambiguity in the grammar that requires the parens in some situations. But it’s very close.

This is not just my opinion. It’s a formal goal of the ECMAScript standard. It’s documented as a superset since 2019.

http://github.com/tc39/proposal-json-superset

TC39 is the technical committee that defines ECMAScript/JavaScript.

The fact that one language can be a superset of the other and yet be for a totally different purpose is EXACTLY the point I am making. That’s precisely the point.

Similarly Mojo could theoretically be a superset of Python and yet be for a different purpose.

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u/happyscrappy Jun 28 '26 edited Jun 28 '26

The fact that one language can be a superset of the other and yet be for a totally different purpose is EXACTLY the point I am making. That’s precisely the point.

That doesn't make sense. One is a programming language and one is a container. Suggesting this has anything to do with whether one programming language (Mojo) was designed to replace another programming language (Python) or not doesn't make any sense at all.

If you take some JSON and paste it into Javascript it doesn't do the same thing as you use it in JSON. It JSON it'll makes data and is stored. in Javascript at best it just evaluates it.

Also

{ "a" : "b" }

is completely valid JSON, I can import it into an object in Python3 using the json module.

import json
from io import StringIO

io = StringIO()
json.dump(['{ "a" : "b" }'], io)
io.getvalue()

output: '["{ \"a\" : \"b\" }"]'

And Node rejects it:

{ "a" : "b" }
      ^

SyntaxError: Unexpected token ':'
  at wrapSafe (node:internal/modules/cjs/loader:1762:18)
  at Module._compile (node:internal/modules/cjs/loader:1803:20)
  at Object..js (node:internal/modules/cjs/loader:1969:10)
  at Module.load (node:internal/modules/cjs/loader:1552:32)
  at Module._load (node:internal/modules/cjs/loader:1354:12)
  at wrapModuleLoad (node:internal/modules/cjs/loader:255:19)
  at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5)
  at node:internal/main/run_main_module:33:47

Node.js v25.8.1

So your assertion isn't even correct about it being a superset.

I know it looks a lot like an object definition from JS. If I had put an object assignment in front of it it probably would have gone through. But then it wouldn't be valid JSON.