Is Ruby a functional language?

Question

Wikipedia says Ruby is a functional language, but I\'m not convinced. Why or why not?

Answer 1

Ruby is a multi-paradigm language that supports a functional style of programming.

Answer 2

Please, have a look at the beginning of the book: "A-Great-Ruby-eBook". It discusses the very specific topic you are asking. You can do different types of programming in Ruby. If you want to program like functionally, you can do it. If you want to program like imperatively, you can do it. It is a definition question how functional Ruby in the end is. Please, see the reply by the user camflan.

Answer 3

I most definitely think you can use functional style in Ruby.

One of the most critical aspects to be able to program in a functional style is if the language supports higher order functions... which Ruby does.

That said, it's easy to program in Ruby in a non-functional style as well. Another key aspect of functional style is to not have state, and have real mathematical functions that always return the same value for a given set of inputs. This can be done in Ruby, but it is not enforced in the language like something more strictly functional like Haskell.

So, yeah, it supports functional style, but it also will let you program in a non-functional style as well.

Answer 4

Whether a language is or is not a functional language is unimportant. Functional Programming is a thesis, best explained by Philip Wadler (The Essence of Functional Programming) and John Hughes (Why Functional Programming Matters).

A meaningful question is, 'How amenable is Ruby to achieving the thesis of functional programming?' The answer is 'very poorly'.

I gave a talk on this just recently. Here are the slides.

Answer 5

It depends on your definition of a “functional language”. Personally, I think the term is itself quite problematic when used as an absolute. The are more aspects to being a “functional language” than mere language features and most depend on where you're looking from. For instance, the culture surrounding the language is quite important in this regard. Does it encourage a functional style? What about the available libraries? Do they encourage you to use them in a functional way?

Most people would call Scheme a functional language, for example. But what about Common Lisp? Apart from the multiple-/single-namespace issue and guaranteed tail-call elimination (which some CL implementations support as well, depending on the compiler settings), there isn't much that makes Scheme as a language more suited to functional programming than Common Lisp, and still, most Lispers wouldn't call CL a functional language. Why? Because the culture surrounding it heavily depends on CL's imperative features (like the LOOP macro, for example, which most Schemers would probably frown upon).

On the other hand, a C programmer may well consider CL a functional language. Most code written in any Lisp dialect is certainly much more functional in style than your usual block of C code, after all. Likewise, Scheme is very much an imperative language as compared to Haskell. Therefore, I don't think there can ever be a definite yes/no answer. Whether to call a language functional or not heavily depends on your viewpoint.

Answer 6

Recursion is common in functional programming. Almost any language does support recursion, but recursive algorithms are often ineffective if there is no tail call optimization (TCO).

Functional programming languages are capable of optimizing tail recursion and can execute such code in constant space. Some Ruby implementations do optimize tail recursion, the other don't, but in general Ruby implementations are not required to do TCO. See Does Ruby perform Tail Call Optimization?

So, if you write some Ruby functional style and rely on TCO of some particular implementation, your code may be very ineffective in another Ruby interpreter. I think this is why Ruby is not a functional language (neither is Python).