What is a functional programming language?

http://enfranchisedmind.com/blog/posts/what-is-a-functional-programming-language/

by bendmorris • 16 years ago

50 26 16 years ago

knowtheory3• 16 years ago

I think we would be remiss to mention that fundamentally the Lambda Calculus and Turing Machines are mathematically equivalent, as proved in the Church-Turing Thesis (http://en.wikipedia.org/wiki/Church%E2%80%93Turing_thesis ).

And while it is true that there are functional features that are unsupported in the basic syntax of imperative languages, you can still do equivalent computation, and after all "Whoever does not understand LISP is doomed to reinvent it" :P

cyrus_4• 16 years ago

54. Beware of the Turing tar-pit in which everything is possible but nothing of interest is easy.

—Alan Perlis, Epigrams on Programming

knowtheory3• 16 years ago

ha, that's great.

I have to say learning about Lisp and the Lambda Calculus renewed my interest in computation and programming back in university. I really find Turing machines quite dull.

Perhaps i did not adequately disclaim my statements though. Having to hack a LISP into your imperative language is neither easy, maintainable or recommended. Just cause you can do it, doesn't mean you should ;)

The rest of the epigrams:

http://www-pu.informatik.uni-tuebingen.de/users/klaeren/epig...

Zak• 16 years ago

The author claims that Clojure tries to do OO. While Clojure does allow interaction with Java's object model, I think it's quite a stretch to say that it tries to do OO. Use of Java interop features for purposes other than interacting with a Java library or framework is generally discouraged.

swannodette• 16 years ago

The article is a year and a half old. Clojure doesn't "try" to do OO- multimethods always worked pretty well, and with 1.2.0 it does OO very well.

Clojure design philosophy is essentially "OOP: The Good Parts".

peregrine• 16 years ago

As someone new to clojure I gotta say that multimethods are pretty nice.

mahmud• 16 years ago

For there to be "Good Parts" of OOP, there would have to be a single kind of OOP.

P.S. Smalltalk.

cyrus_4• 16 years ago

The lambda calculus admits no notion of mutability, while the Turing machine is all about mutating locations on a tape. So I would argue that functional programming is really about immutability.

A language is a functional programming language if its standard library includes and is written specifically for immutable data structures. Mutable data structures, if they exist, are second class citizens.

Whether there is an object system is completely orthogonal. Whether there are first-class functions is also completely orthogonal.

jmillikin4• 16 years ago

This is a very odd definition; it would exclude many languages typically considered "functional", such as Haskell.

cyrus_4• 16 years ago

Haskell's core data structures are immutable (ADTs, tuples, records, etc.) -- what do you mean?

Dn_Ab• 16 years ago

I think there are about two classes roughly. The mathematically pure functions crowd with emphasis on correctness and the expressive power camp (which also helps with correctness indirectly).

I fall in the latter camp where functional programming is an approach, a style if you would. Where there are first order functions and the ability to easily manipulate them (C# fails here via verbosity), partial function application (often mislabelled currying), closures, recursion is forefront and immutability is the default. Terseness, algebraic types, tuples and pattern matching are optional but highly recommended (in my opinion Scala and Erlang are not terse relatively, Haskell/F#/Clojure are). I also find inference with static typing to be useful. [edit: by terse I don't mean by lines of code but vaguely, how busy each line is].

This combination leads to an extremely powerful and different way of thinking about and writing code that gives extensibility, composability and isolation for free. A style built around passing and assigning functions - treating functions the way most people treat variables. It also allows you to easily render abstractions of your problems without fussing with boiler plates. In terms of organizing and encapsulation it falls short but these new hybrids are shoring things up.

primodemus• 16 years ago

If we define a functional language as a language based on the lambda calculus, then whether it has first-class functions or not is not completely orthogonal since functions are values in the lambda calculus.

scottjad• 16 years ago

Functional means whatever the person saying it means by it.

Trying to give an all or nothing definition is doomed to failure and counter-examples.

knowtheory3• 16 years ago

“When I use a word,” Humpty Dumpty said, in a rather a scornful tone, “it means just what I choose it to mean—neither more nor less.”

“The question is,” said Alice, “whether you can make words mean so many different things.”

“The question is,” said Humpty Dumpty, “which is to be master that’s all.”

Alice was too much puzzled to say anything, so after a minute Humpty Dumpty began again. “They’ve a temper, some of them—particularly verbs, they’re the proudest—adjectives you can do anything with, but not verbs—however, I can manage the whole lot! Impenetrability! That’s what I say!”

and just for completenesses sake:

Alan Perlis — 48. The best book on programming for the layman is "Alice in Wonderland"; but that's because it's the best book on anything for the layman.

rufus_t• 16 years ago

It, and "Through the Looking-glass", are very good books on programming for programmers, too. If you haven't read them since you were liddle, you're missing out.

gtani• 16 years ago

FP means different to lispers, ML'ers and typeclassists (haskell, scala). Here's my attempt at a def

http://news.ycombinator.com/item?id=2075192

What is a functional programming language?

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