Should I learn Haskell or F# if I already know OCaml?

Question

I am wondering if I should continue to learn OCaml or switch to F# or Haskell.

Here are the criteria I am most interested in:

• Longevity

  • Which language will last longer? I don't want to learn something that might be abandoned in a couple years by users and developers.
  • Will Inria, Microsoft, University of Glasgow continue to support their respective compilers for the long run?

• Practicality

  • Articles like this make me afraid to use Haskell. A hash table is the best structure for fast retrieval. Haskell proponents in there suggest using Data.Map which is a binary tree.
  • I don't like being tied to a bulky .NET framework unless the benefits are large.
  • I want to be able to develop more than just parsers and math programs.

• Well Designed

  • I like my languages to be consistent.

Please support your opinion with logical arguments and citations from articles. Thank you.

Answer 1

F# and OCaml are very similar in syntax, though, obviously, F# is better with .NET.

Which one you learn or use should be dependent on which platform you are aiming for.

In VS2010 F# is going to be included, and since it compiles to .NET bytecode, it can be used on a windows OS that supports the .NET version you used for it. This will give you a large area, but there are limits, currently with F# that OCaml don't have, in that F# appears not to take advantage of all the processors on a machine, but, that is probably due to F# still being developed, and this may be a feature that isn't as important yet.

There are other functional languages, such as Erlang that you could look at, but, basically, if you are strong in one FP language then you should be able to pick up another fairly quickly, so, just pick one that you like and try to develop interesting and challenging applications in it.

Eventually language writers will find a way to get OO languages to work well with multi-cores and FP may fall to the wayside again, but, that doesn't appear to be happening anytime soon.

Answer 2

There's no simple answer to that question, but here are some things to consider:

Haskell and OCaml are both mature languages with strong implementations. Actually, there are multiple good implementations of Haskell, but I don't think that's a major point in its favor for your purpose.

F# is much younger, and who can predict where Microsoft will decide to take it? How you feel about that depends more on how you feel about Microsoft than anything anyone can tell you about programming languages.

OCaml (or ML in general), is a good practical language choice that supports doing cool functional stuff without forcing you to work in a way that might be uncomfortable. You get the full benefit of things like algebraic data types, pattern matching, type inference, and everybody else's favorite stuff. Oh, and objects.

Haskell gives you all that (except objects, pretty much), but also more or less forces you to rethink everything you think you know about programming. This might be a very good thing, if you're looking to learn something new, but it might be more than you want to bite off. I say this as someone who is only maybe halfway along the path to being a productive, happy Haskell programmer.

Both OCaml and Haskell are being used to write lots of different kinds of programs, not just compilers and AI or whatever. Google is your friend.

One last note: OCaml gives you hashtable, but it's hardly sensible to use it in code if you really want to embrace functional programming. Persistent trees (like Data.Map) are really the right solution for Haskell, and have lots of nice properties, which is one of the cool things to learn about when you pick up Haskell.

Answer 3

Longevity

No one can predict the future, but

• OCaml and Haskell have been surving well for a number of years, which bodes well for their future
• when F# ships with VS2010, MS will have legal obligations to support it for at least 5 years

Practicality

Perf: I don't have enough first-hand experience with Haskell, but based on second-hand and third-hand info, I think OCaml or F# are more pragmatic, in the sense that I think it is unlikely you'll be able to get the same run-time perf in Haskell that you do in OCaml of F#.

Libraries: Easy access to the .Net Framework is a huge benefit of F#. You can view it as being "tied to this bulky thing" if you like, but don't forget that "you have access to a huge bulky library of often incredibly useful stuff". The 'connectivity' to .Net is one of the big selling points for F#. F# is younger and so has fewer third-party libraries, but there is already e.g. FsCheck, FParsec, Fake, and a bunch of others, in addition to the libraries "in the box" on .Net.

Tooling: I don't have enough personal experience to compare, but I think the VS integration with F# is superior to anything you'll find for OCaml/Haskell today (and F# will continue to improve a bit here over the next year).

Change: F# is still changing as it approaches its first supported release in VS2010, so there are some breaking changes to language/library you may have to endure in the near future.

Well Designed

Haskell is definitely beautiful and consistent. I don't know enough OCaml but my hunch is it is similarly attractive. I think that F# is 'bigger' than either of those, which means more dusty corners and inconsistencies (largely as a result of mediating the impedence mismatch between FP and .Net), but overall F# still feels 'clean' to me, and the inconsistencies that do exist are at least well-reasoned/intentioned.

Overall

In my opinion you will be in 'good shape' knowing any of these three languages well. If you know a big long-term project you want to use it for, one may stand out, but I think many of the skills will be transferable (more easily between F# and OCaml than to/from Haskell, but also more easily among any of these three than with, say, Java).

Answer 4

Longevity

• Haskell is de facto the dominant language of functional-programming research. Haskell 98 will last for many more years in stable form, and something called Haskell may last 10 to 30 years---although the language will continue to evolve. The community has a major investment in Haskell and even if the main GHC developers are hit by a bus tomorrow (the famous "bus error in Cambridge" problem), there are plenty of others who can step up to the plate. There are also other, less elaborate compilers.

• Caml is controlled by a small group at INRIA, the French national laboratory. They also have a significant investment, Others are also invested in Caml, and the code is open source, and the compiler is not too complicated, so that too will be maintained for a long time. I predict Caml will be much more stable than Haskell, as the INRIA folks appear no longer to be using it as a vehicle for exploring new language ideas (or at least they are doing so at a smaller rate than in the past).

• Who knows what a company will do? If F# is successful, Microsoft could support it for 20 years. If it is not successful, they could pull the plug in 2012. I can't guess and won't try.

Practicality

A hash table is the best structure for fast retrieval. Haskell proponents in there suggest using Data.Map which is a binary tree.

It depends on what you are searching. When your keys are strings, ternary search trees are often faster than hash tables. When your keys are integers, Okasaki and Gill's binary Patricia trees are competitive with hashing. If you really want to, you can build a hash table in Haskell using the IO monad, but it's rare to need to.

I think there will always be a performance penalty for lazy evaluation. But "practical" is not the same as "as fast as possible". The following are true about performance:

• It is easiest to predict the time and space behavior of a Caml program.

• F# is in the middle (who really knows what .NET and the JIT will do?).

• It is hardest to predict the time and space behavior of Haskell programs.

• Haskell has the best profiling tools, and in the long run, this is what yields the best performance.

I want to be able to develop more than just parsers and math programs.

For an idea of the range of what's possible in Haskell, check out the xmonad window manager and the vast array ofpackages at hackage.haskell.org.

I don't like being tied to a bulky .NET framework unless the benefits are large.

I can't comment:

Well Designed

I like my languages to be consistent.

Some points on which to evaluate consistency:

• Haskell's concrete syntax is extremely well designed; I'm continually impressed at the good job done by the Haskell committee. OCaml syntax is OK but suffers by comparison. F# started from Caml core syntax and has many similarities.

• Haskell and OCaml both have very consistent stories about operator overloading. Haskell has a consistent and powerful mechanism you can extend yourself. OCaml has no overloading of any kind.

• OCaml has the simplest type system, especially if you don't write objects and functors (which many Caml programmers don't, although it seems crazy to me not to write functors if you're writing ML). Haskell's type system is ambitious and powerful, but it is continually being improved, which means there is some inconsistency as a result of history. F# essentially uses the .NET type system, plus ML-like Hindley-Milner polymorphism (See question "What is Hindley-Milner".)

• OCaml is not quite consistent on whether it thinks variants should be statically typed or dynamically typed, so it provides both ("algebraic data types" and "polymorphic variants"). The resulting language has a lot of expressive power, which is great for experts, but which construct to use is not always obvious to the amateur.

• OCaml's order of evaluation is officially undefined, which is a poor design choice in a language with side effects. Worse, the implementations are inconsistent: the bytecoded virtual machine uses one order and the native-code compiler uses the other.

Answer 5

This wasn't one of your criteria but have you considered job availability? Haskell currently list 144 jobs on indeed, Ocaml list 12 and C# list 26,000. These numbers are not perfect but I bet you that once F# ships it won't be long before it blows past Haskell and Ocaml in the number of job listings.

So far every programming language included in Visual Studios has thousands of job listings for it. Seems to me that if you want the best chance to use a functional programming language as your day job then F# will soon be it.

Answer 6

Should you learn F# or Haskell if you know OCaml?

I believe the answer is certainly yes, ideally you should learn all three languages because each one has something to offer but F# is the only one with a significant future so, if you can only feasibly learn one language, learn F# by reading my Visual F# 2010 for Technical Computing book or subscribing to our The F#.NET Journal.

Longevity

Microsoft committed to supporting F# when they released it as part of Visual Studio 2010 in April. So F# is guaranteed a rosy future for at least a few years. With a powerful combination of practically-important features like a high performance native-code REPL, high-level constructs for parallelism built-in to .NET 4 and a production-quality IDE mode, F# is a long way ahead of any other functional programming language in terms of real world applicability now. Frankly, nobody is even working on anything that might be able to compete with F# in the near future. My own open source HLVM project is an attempt to do so but it is far from ready.

In contrast, both OCaml and Haskell are being developed in extremely unproductive directions. This has been killing OCaml for several years now and I expect Haskell to follow suit over the next few years. Most former professional OCaml and Haskell programmers already moved on to F# (e.g. Credit Suisse, Flying Frog Consultancy) and most of the rest will doubtless migrate to more practical alternatives such as Clojure and Scala in the near future.

Specifically, OCaml's QPL license prevents anyone else from fixing its growing number of fundamental design flaws (poor 32-bit support, very poor shared-memory parallelism, no value types, slow parametric polymorphism, interpreted REPL, cumbersome FFI etc.) because they must distribute derivative works only in the form of patches to the original and the Debian package maintainers refuse to acknowledge an alternative upstream. The new features being added to the language, such as first-class modules in OCaml 3.12, are nowhere near as valuable as multicore capability would have been.

Some projects were started in an attempt to save OCaml but they proved to be too little too late. The parallel GC is practically useless and David Teller quit the batteries included project (although it has been picked up and released in a cut-down form). Consequently, OCaml has gone from being the most popular functional language in 2007 to severe decline today, with caml-list traffic down over 50% since 2007.

Haskell has fewer industrial users than OCaml and, although it does have multicore support, it is still being developed in a very unproductive direction. Haskell is developed almost entirely by two people at Microsoft Research in Cambridge (UK). Despite the fact that purely functional programming is bad for performance by design, they are continuing to try to develop solutions for parallel Haskell aimed at multicores when the massive amounts of unnecessary copying it incurs hits the memory wall and destroys any hope of scalable parallelism on a multicore.

The only major user of Haskell in industry is Galois with around 30 full-time Haskell programmers. I doubt they will let Haskell die completely but that does not mean they will develop it into a more generally-useful language.

Practicality

I wrote the article you cited about hash tables. They are a good data structure. Other people have referred to purely functional alternatives like ternary trees and Patricia trees but these are usually ~10× slower than hash tables in practice. The reason is simply that cache misses dominate performance concerns today and trees incur an extra O(log n) pointer indirections.

My personal preference is for optional laziness and optional purity because both are generally counter productive in the real world (e.g. laziness makes performance and memory consumption wildly unpredictable and purity severely degrades average-case performance and makes interoperability a nightmare). I am one of the only people earning a living entirely from functional programming through my own company. Suffice to say, if I thought Haskell were viable I would have diversified into it years ago but I keep choosing not to because I do not believe it is commercially viable.

You said "I don't like being tied to a bulky .NET framework unless the benefits are large". The benefits are huge. You get a production-quality IDE, a production-quality JIT compiler that performs hugely-effective optimizations like type-specializing generics, production-quality libraries for everything from GUI programming (see Game of Life in 32 lines of F#) to number crunching. But the real benefit of .NET, at least for me, is that you can sell the libraries that you write in F# and earn lots of money. Nobody has ever succeeded selling libraries to OCaml and Haskell programmers (and I am one of the few people to have tried) but F# libraries already sell in significant quantities. So the bulky .NET framework is well worth it if you want to earn a living by writing software.

Well designed

These languages are all well designed but for different purposes. OCaml is specifically designed for writing theorem provers and Haskell is specifically designed for researching Haskell. F# was designed to address all of the most serious practical problems with OCaml and Haskell such as poor interoperability, lack of concurrent garbage collection and lack of mature modern libraries like WPF in order to bring a productive modern language to a large audience.

Answer 7

This is not directly related to the OP's question as to whether or not to learn F#, but rather, an example of real world OCaml usage in the financial sector: http://ocaml.janestreet.com/?q=node/61

Very interesting talk.