[reikonomusha]

They did parse it, albeit indirectly, by Racket’s reader. Co2 is a language, not a bunch of function calls, so it’s not quite the same as building a library in your favorite language. The article even gives examples of new syntax they produced.

Parsing Lisp in Lisp is so easy because it’s free.

[cheez]

https://github.com/dustmop/co2/blob/master/compile.scm#L3689

Indeed, it's almost trivial.

[lispm]

you just need to implement read-syntax ...

[cheez]

I wasn't being sarcastic, it was very simple the way they've done it. https://docs.racket-lang.org/reference/Reading.html#%28def._...

[lispm]

I'm saying that there is a larger machinery behind it. It just looks simple.

[cheez]

Well ok but then technically a hello world is complex for the same reasons

[lispm]

I'd say this depends of the complexity of the I/O system.

This was the original claim, which you supported:

'Parsing Lisp in Lisp is so easy because it’s free.'

The example you were pointing to is explicitly calling a parsing engine of Racket via 'read-syntax'. Actually more complicated than the usual s-expression reader - which does only read s-expressions, but has no further idea about Scheme syntax.

Check the usual Scheme report / Racket documentation for the definition of Scheme syntax, syntax objects and its extension mechanisms (macros, ...). I'd say the whole thing is non-trivial. There is a grammar of Scheme, but it is not fixed, because there are extension mechanisms, which make parsing challenging.

It's 'free' because it's a provided language facility - but not free in terms of complexity of the concepts to understand.

And no, the syntax of s-expressions (-> data) is not the syntax of Lisp. It's just the syntax of s-expressions. Search the Scheme report for 'syntax'...

[lispm]

> Parsing Lisp in Lisp is so easy because it’s free.

You just have to implement an s-expression reader.

Plus an interpreter, compiler or a code walker, which can actually parse the Lisp code.

[colejohnson66]

> Parsing Lisp in Lisp is so easy because it’s free.

Are there any other languages that have this feature? I.E. where the data and the code are the same syntax?

[guicho271828]

Well, if there is new such language then it would be eventually called a lisp dialect.

[kayamon]

Rebol springs to mind.