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Comment by aidenn0 | Hacker News Reader

What is "not data" that can be the result of eval; at first I thought he was talking about side effects, but 5 minutes after he first said that I'm still not sure what he was talking about.

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Clojure has facilities for seamless interop with Java (or whatever platform it's hosted on). A lot of times when inter-operating with Java libraries, you get back an opaque Object with associated methods when you'd normally expect a transparent Clojure map or some other pure data structure if you were interacting with a purely Clojure library. Datafy is just a protocol that allows you to transform those opaque Objects into transparent data structures.

Clojure separates data from the functions that operate on it. In contrast, Objects intertwine those two things. You can roughly think of the "data" part of an Object as its attributes, and the "function" part its methods.

I'm not entirely sure I get the distinction you are making. Sounds like you are just saying that not everything prints well. Which, yeah, that is true. As noted in the speech, sometimes it is just cumbersome to see printed.

I still fail to see how methods are not data in the general sense, but while trying to answer my own question, it seems that "data" in clojure means roughly "Either an atomic type[1] or a collection"

1: an "atom" in clojure is not what it is in traditional lisp lingo; is there a name in clojure for type that is roughly the union of: symbol, number, character, boolean ? perhaps "primitive"?

Within Clojure almost all data is directly serializable to data literals. Java objects don't have this property directly and are guaranteed to exposed everything via methods. Datafy and Nav just give Clojure the power to codify your observations. You're right for the most part, this is just the tools for interop (and a bunch of cool stuff you can build on top of it).

Perhaps “value”? The language is data-oriented, and everything you mentioned in [1] except for “symbol” easily falls within that. In Clojure, a symbol always evaluates to a specific value too, so it seems like a good fit.

A Clojure atom is one of the few types that is not immutable, but the way it is updated is pretty strictly enforced by the language, and references to it at any given point in time are still immutable.

I don’t have any insight into your broader question.

This concept is pretty subtle. Rich Hickey does a great job at explaining it (as always) in "Are We There Yet?"[1]. He deconstructs objects into state (attributes) and behavior (methods), and then uses values (or data) to represent state, and functions to represent behavior. Give that a watch a couple of times to get a better handle on what all this means from the Clojure perspective.

[edit] To answer your other question, a value that isn't a collection in Clojure is called a scalar.

1: https://www.infoq.com/presentations/Are-We-There-Yet-Rich-Hi...

Oh, so in TFA, Stuart is using the term "data" to mean "Value" in the sense that Rich talks about (Are We There Yet is only one of of many of his talks about values (I think he had one called something like The Value of Values).

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