> What I mean by “code in an object language is data in the metalanguage” is that, in the metalanguage in which you're writing a compiler or interpreter, the object language program that you're processing is represented as a data structure (say, as a syntax tree). It's just a triviality, I'm not saying anything really deep.
I understood what you were saying, and didn't ask for an explanation. I just don't see why you felt the need to correct me on my calling first=class functions "code as data" and substitute your own definition that had nothing to do with what I was saying.
> My definition of functional programming is “using (procedures that compute) mathematical functions whenever possible”. A mathematical function is a mapping from values to values, so if a language doesn't have a good notion of (possibly compound) value, then you're going to run into trouble writing procedures that compute mathematical functions.
Again, I didn't ask what your definition was, because it wasn't relevant to the conversation.
You're basically interrupting me to tell me I'm not using the same definitions of words as you are, and it's not particularly endearing. If you don't understand what I'm saying, I'll be happy to explain. If you do, however, understand what I'm saying well enough to correct me on my usage of the English language, then my usage of the language has been clear enough for my goals, so I wouldn't be interested in your corrections even if they represented HN's common usage (which they don't).
> I just don't see why you felt the need to correct me on my calling first=class functions "code as data"
Because first-class functions aren't “code as data”. When you have a first-class function, the only thing you can do with it is call it. If it were a data structure, you could analyze its constituent parts.
> You're basically interrupting me to tell me I'm not using the same definitions of words as you are,
The Wikipedia article you linked says:
“In computer science, functional programming is a programming paradigm—a style of building the structure and elements of computer programs—that treats computation as the evaluation of mathematical functions [emphasis mine] and avoids changing-state and mutable data.”
The emphasized part is just what I said. That a mathematical function is a mapping from values to values is unquestionable - it's not something I'm saying, it's a mathematical fact. So if you can't express compound values, you're limited to a world where mathematical functions can only manipulate primitive values.
> Because first-class functions aren't “code as data”. When you have a first-class function, the only thing you can do with it is call it. If it were a data structure, you could analyze its constituent parts.
There are lots of ways in which you can treat a first class function as data, even if it can't be treated 100% equivalently to data in every single situation. You can, for example, pass it to other functions like data. Sure, most languages don't let you inspect the internals, but that's only one way of treating code as data.
> The emphasized part is just what I said. That a mathematical function is a mapping from values to values is unquestionable - it's not something I'm saying, it's a mathematical fact. So if you can't express compound values, you're limited to a world where mathematical functions can only manipulate primitive values.
I said, "And to be honest, other languages have done a lot better things with the functional programming aspects of Common Lisp." Common Lisp isn't a purely functional language, but it does have functional aspects. Note in the article I quoted, that Common Lisp is the first language listed in the "prominent programming languages which support functional programming such as" section.
You're literally not even disagreeing with me, you're just defining "functional programming language" as "purely functional programming language", when I literally never even called Common Lisp a functional programming language.
Insisting on your definitions instead of trying to understand what I said doesn't make me want to engage with you further.
> There are lots of ways in which you can treat a first class function as data, even if it can't be treated 100% equivalently to data in every single situation. You can, for example, pass it to other functions like data.
Strictly speaking, you can't pass functions as data. You can only pass thunks that, when forced, yield functions. A thunk is data, but a function is a computation. Computations are “too active” to be stored or passed around unthunked. The technical details are here: http://www.cs.bham.ac.uk/~pbl/cbpv.html, http://www.cs.bham.ac.uk/~pbl/papers/. (I am not the owner of the website, just in case.)
> Sure, most languages don't let you inspect the internals, but that's only one way of treating code as data.
What are the others?
> You're literally not even disagreeing with me, you're just defining "functional programming language" as "purely functional programming language",
How did you conclude that? I never said anything of the sort. What I said is “functional programming is programming with procedures that compute mathematical functions whenever possible”. Pure functional programming imposes further requirements, like effect segregation (as in Haskell) or even the total absence of effects (obviously unsuitable for a general-purpose language). FWIW, I'd count ML, Racket, Clojure and Erlang as functional languages.
> when I literally never even called Common Lisp a functional programming language.
You said Common Lisp has “functional aspects”. Well, closures make a language higher-order, but so do Java-style objects! For a language to be called “functional”, however, it has to make functional programming actually pleasant. I showed one fundamental limitation of Common Lisp in this regard: you can't define functions that take or return compound values, because Common Lisp doesn't have compound values in the first place.
I understood what you were saying, and didn't ask for an explanation. I just don't see why you felt the need to correct me on my calling first=class functions "code as data" and substitute your own definition that had nothing to do with what I was saying.
> My definition of functional programming is “using (procedures that compute) mathematical functions whenever possible”. A mathematical function is a mapping from values to values, so if a language doesn't have a good notion of (possibly compound) value, then you're going to run into trouble writing procedures that compute mathematical functions.
Again, I didn't ask what your definition was, because it wasn't relevant to the conversation.
You're basically interrupting me to tell me I'm not using the same definitions of words as you are, and it's not particularly endearing. If you don't understand what I'm saying, I'll be happy to explain. If you do, however, understand what I'm saying well enough to correct me on my usage of the English language, then my usage of the language has been clear enough for my goals, so I wouldn't be interested in your corrections even if they represented HN's common usage (which they don't).