Re: [Haskell-cafe] Re: Haskell vs OCaml

Marcin gives a good capsule description of the differences between ocaml and haskell. Let me add my two cents. I also learned ocaml before learning haskell, and the biggest single difference I found is that haskell is a lazy, purely functional language and ocaml is a strict, "mostly functional" language. So all the IO monad stuff in haskell doesn't exist in ocaml -- writing imperative code in ocaml is much like writing imperative code in C, albeit with different syntax. This makes it much easier to transition to for C or python programmers, but it's easy for side-effects to work their way into your program without you realizing it, which means you lose a lot of the advantages of functional programming -- unless you take a lot of care to make sure that most of your functions are in fact purely functional (and the compiler won't help you with that). Another big difference between ocaml and haskell is that haskell has type classes and ocaml does not. You can't imagine how great type classes are until you start using them. They mirror so much of what you intend a function to be in the type of the function, and they also allow you to use functions in a much broader domain than you would expect. Basically (if you don't know this already), type classes give you overloading of functions and operators on new data types, all done at compile time. Ocaml, in contrast, has "functors" which allow you to create customized versions of data structures parameterized on almost anything, but the data structure you create is a full module. This is also pretty elegant, but IMO is much more heavyweight and doesn't have the syntactic advantages of haskell's type classes. Since ocaml doesn't have monads at all, a lot of the more advanced monadic programming that haskellers like to do is much more cumbersome to do in ocaml. However, the biggest advantage that ocaml has over haskell is that for most applications, an ocaml program will run faster, perhaps a lot faster, than an equivalent haskell program (although the haskell program may be much smaller, have fewer bugs, be prettier, etc.). That's because lazy evaluation in haskell requires the system to wrap closures around unevaluated code and evaluate it later. This has a cost, and it simply isn't there in ocaml. If you find functional programming *completely* baffling, learning haskell off the bat is like jumping into the deep end of the swimming pool. Learning a language like ocaml first can be a good stepping stone to haskell, since many of the core concepts (like algebraic data types) are basically the same. Scheme is another great language to learn FP from, preferably in conjunction with a good textbook like _How to Design Programs_ (http://www.htdp.org) or _Structure and Interpretation of Computer Programs_ (http://mitpress.mit.edu/sicp). My progression was scheme -> ocaml -> haskell, which was nice because I didn't have to add nearly as much new material at each stage as I would have had to had I learned e.g. haskell before learning scheme or ocaml. Mike

From: Marcin 'Qrczak' Kowalczyk Mail-Followup-To: haskell-cafe@haskell.org Date: Tue, 03 May 2005 20:38:14 +0200

John Goerzen writes:

...

I'd say that there are probably no features OCaml has that Haskell lacks that are worth mentioning.

Its type system has some interesting features: polymorphic variants, parametric modules, labeled and optional arguments, objects, variance annotations of type parameters used for explicit subtyping.

It has more convenient exceptions: the exn type can be extended with new cases which look like variants of algebraic types.

There is camlp4 for extending the syntax or changing it completely.

OTOH Haskell provides type classes, better integrated arbitrary precision integer type, type variables with kinds other than *, polymorphic recursion, much better FFI, and with GHC extensions: universal and existential quantifiers in function types (OTOH OCaml recently got universal quantifiers in record fields), GADTs, implicit parameters, template Haskell.

-- __("< Marcin Kowalczyk \__/ qrczak@knm.org.pl ^^ http://qrnik.knm.org.pl/~qrczak/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe