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Comment by greydius | Hacker News Reader

Most people would agree that in functional programming we can pass functions around as first class objects. What we disagree on is the definition of function.

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That's just one aspect of functional programming. By that definition, almost any modern language is functional.

Every modern language is functional. :P But more accurately, every modern language is generally multi-paradigm.

Take it from the other side: why would a language that allows to create higher-order functions/closures not be called functional?

Because that makes the term meaningless. You may as well ask "why don't we call any language that lets you do two actions in sequence 'procedural'?"

A term does not necessarily become meaningless when it applies to a lot of things. "Functional" might be a broad category after all, not the exclusive name of a subset of functional languages. And if your language allows different paradigms, it will be called "functional and imperative and object-oriented... ". At best, if a property is so common that most language have it, it can be assumed to be satisfied by default. As for "procedural", the definition on wikipedia is a little more precise and does not apply to all languages: https://en.wikipedia.org/wiki/Procedural_programming.

That doesn't make the term meaningless, it just means that "functional programming" is a victim of its own success.

If you can apply the term to every programming language in widespread use today[1], then yes, it is pretty useless. There is real value in having the term "functional programming" be meaningful and denote a certain class of languages; defining that as "any language with first-class function values" is too broad as to render the term meaningless.

[1] Even C has this with Apple's Blocks extension (http://clang.llvm.org/docs/Block-ABI-Apple.html).

Most languages only have higher-order procedures, not higher-order functions.

As for closures, well, closures are an implementation technique. Not distinguishing between language features and implementation techniques is a part of an established tradition that comes from Lisp, but that doesn't make it any less wrong.

> Most languages only have higher-order procedures, not higher-order functions.

What do you mean by that?

Functions have the following properties:

(0) A function maps every element of its domain to a unique element of its codomain.

(1) Functions don't exist in time, let alone change over time.

(2) Two functions with the same domain and codomain are equal if they map the same domain elements to the same codomain elements.

Since when do so-called “first-class functions” in most programming languages behave like this?

No, wrong. You can pass pointers to functions in C.

It is a bit snarky, but also has a ground truth: pointers to functions aren't functions.

More importantly, you cannot make functions in C. For example, one cannot write a function that, given pointers to functions that compute 1/x and sin(x), returns a pointer to a function that returns 1/sin(x)

That's not a function, that's a closure. And you can simulate that in C by creating a struct that contains the function pointer and the set of captured data (and then when you invoke the function you pass the struct to it as a parameter).

Yes, hence the distinction between first-class features and others, which you have to implement yourself.

The parent comment said C function pointers aren't functions. They are. They just aren't closures.

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