Can Ruby really be used as a functional language?

Question

Can Ruby really be used as a functional language? What are some good tutorials to teach this facet of the language? Note: I really want to use and stick with Ruby as my primary language so I am not interested at this point in being converted to YAFL (yet another functional language). I am really interested in how well Ruby's functional facets perform against the standard functional language baseline. Thanks.

Answer 1

Yes...sort of. Ruby lacks a reasonable construct to enforce immutability. (Object#freeze doesn't count) Immutability is really the cornerstone of functional languages. Further, Ruby's core libraries are highly oriented toward imperative design. Its Array and Hash classes are both mutable by nature, even String has methods which make non-immutable (e.g. gsub!). Ironically, Java is more "functional" than Ruby in this respect.

With that said, it is possible to do functional-like programming in Ruby. Any time you use a block/proc/lambda, you are using a feature that comes from functional programming. Likewise, collection methods like map and zip are also higher-order constructs which find their roots in languages like Lisp, ML and Haskell.

If you really want to do functional programming, you will want to use a language which is more geared toward that genre. Some suggestions:

• Clojure - Since you phrased the question using Ruby, I'm guessing you're of the dynamically typed persuasion. Clojure is like a strictly-functional Lisp that runs on the JVM.
• F# - Basically OCaml on the CLR. Very nice, very clean
• Scala - Not a strictly functional language, but much better for it than Ruby
• Haskell - Everybody's favorite!

You'll notice that three of these four languages are statically typed. In fact, in the case of Scala and Haskell, these are very statically typed languages (much stronger type systems than, say, Java). I'm not sure why this is a trend in functional languages, but there you have it.

Answer 2

It depends what you mean by "Functional Programming". In my view, the most important thing is that functions are first class values, and in this respect Ruby is a functional language.

Answer 3

It has a fairly comprehensive set of list comprehensions - see Martin Fowler's article. However, it's type system is not as powerful as the likes of Haskell. Also, its focus is not on immutability, as is typical for functional languages.