Liu shuping wrote:

I am new to Haskell, currently I am doing .Net development on windows platform. I began to know about Haskell for the reason when I knew some C# lambda features come from functional language. I am interested in Haskell from the very beginning when I saw it.

Hello there and welcome to the Haskell world. First of all, Haskell is a general purpose language, so you can write any kind of problem. But of course this is only half of the story.

For I am really a very beginner, I get some basic questions: 1. Can you have some very general information to explain why use Haskell or functional language.

There are lots of pages on the WWW explaining "why functional programming (FP) matters" (this is the name of one of them). To give a short summary: FP gives you less programming errors, less code to type and more readable code (to FP programmers, of course). Also modern FP languages give you sophisticated type systems. Languages like C#, D and Java approach this, but are far from comparable.

2. Is it a right choice of Haskell if I want to develop some geology software which mainly doing some huge numerical computation which takes long long time?

Probably yes. There are a few libraries for fast numerical calculations, including bindings to well known number crunching packages. If your favorite package is not among those, you can easily make a binding on your own using the foreign function interface. This is very easy. Regarding performance: If you used to develop in C#, don't worry too much. Your Haskell programs will probably be faster.

3. How about user interface, is Haskell capable to build application with complex user interface? or should I just use Haskell to build the core engine and user other language to build the user interface?

There are two major library bindings: Gtk2hs and wxHaskell. You can use them to build any type of graphical user interface portably.

4. Is Haskell cross-platform? I mean if the Haskell source code is "code once and build everywhere?"

Much more than C#. In general, unless you use OS-specific functions, you won't have any portability issues.

5. Are there any successful applications built with Haskell? they can give me a direct scene of what Haskell can do.

Nothing very big yet. Darcs is an excellent version control system. GHC is the most mature Haskell compiler. Xmonad is a simple window manager for X. There is also Frag, a small 3D shooter (essentially a tech demo). Finally I would mention Happstack, a complete framework for rapid and safe web development. Now as I've noted above, this is only half of the story. The Haskell user base is much smaller than the user bases of the most popular languages, so there are less libraries and less applications. One reason for this is that Haskell has a steep learning curve. Many Haskell programmers find that in the first few days or even weeks they do much more learning than actual programming. Not that they couldn't get applications done, but Haskell is all about safety and correctness, so you want to learn to do it properly instead of just doing it, like you would in, say, PHP. This is why we say Haskell is valuable to know, even if you don't use it. Note that other languages are slowly adopting Haskell concepts. This can be seen most clearly in Microsoft's F# language. It's nowhere near Haskell, but you can see a lot of inspiration. It has very similar syntax, algebraic types, currying and it even employs monadic computations (they call them computation expressions). Conclusion: Go ahead and learn Haskell. Then decide for yourself, whether it's suitable for your project. Don't worry, learning Haskell will always pay off, even if you don't use it. Also don't fear to use languages, which are not widely used. Paul Graham has written a nice anecdote about this [1]. You should definitely read it, it's a true story. [1] http://www.paulgraham.com/avg.html Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/