zaxis writes:

However, i donot know how to write pure function using C style. func1 a = { -- ...; a * 2; -- ...; }

You mean imperatively? Short answer: you can't and you shouldn't. Slightly longer answer: you can possibly fudge something together using the Identity monad from mtl, but that will involve wrapping/unwrapping everywhere. Learn to think about how to chain/group functions together to form more of a "pipeline" rather than a sequence of statements. Haskell =/= C. -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

Hello zaxis, as others have noted, you are trying to write C in Haskell. Well, that gains you nothing and rather gets you into trouble. If you want to write C, then use instead and not Haskell, because the idioms you're used to in C will not work at all in Haskell. Note for example that the 'do' keyword is misleading. It does not introduce imperative code, but monadic code, which may well be pure. To answer your question: There are no blocks in Haskell, which you could put into braces. Don't think in blocks of code, because that is C, not Haskell, and it's plain wrong. You are not going to write any for/while loops anyway. Thinking that way may have a negative impact on your Haskell coding style. The only place where braces are used is record types and many Haskell programmers (including me) consider this an ugly syntax. But don't worry, you'll get used to the new syntax and eventually fall in love with it, because it will make your life easier. I myself came from years of C/C++ experience and had similar difficulties in the beginning. Greets Ertugrul zaxis wrote:

For me i like C style instead of layout. For example, func1 a = do -- ... a * 2 -- ...

I always write it as: func1 a = do { -- ...; a * 2; -- ...; }

However, i donot know how to write pure function using C style. func1 a = { -- ...; a * 2; -- ...; }

will not compile without `do`.

Sincerely!

----- fac n = foldr (*) 1 [1..n]

-- nightmare = unsafePerformIO (getWrongWife >>= sex) http://blog.ertes.de/

Ditto what everyone else has said. But to clarify what's going on: The braces are used to introduce a list of "things", such as monadic actions, data fields, or declarations. For example, consider the following code: f a = let { a_times_2 = a*2; a_times_4 = a*4; } in a_times_2+a_times_4 main = putStrLn $ "f 3 = " ++ show (f 3) The reason why my code compiled and yours didn't is because the compiler saw that the braces were being used to introduce a list of declarations, and the reason why it knew this was because of the "let" keyword. By contrast, in your code it doesn't see a "let", so it assumes that you must be introducing a list of monadic actions. Hence it yells at you for not putting in a "do". Remember that a pure function is merely a definition of what the output is for a given input. It does not say anything about *how* to do this. Thus, you should never think of a pure function as being a list of actions but rather (approximately) a definition which may require some additional declarations (such as introduced by "let") solely for the purpose of making it easier for *you* to *express* what its value is. (I say approximately because the way you express it does affect the way it gets computed despite technically being pure, but this is not something you should be worrying about right now.) But again, even though you could use curly brackets and semicolons as I illustrated above, you really should be using whitespace as it is the standard practice; others reading your code may be confused by their presence and so have to work harder to figure out what is going on. Cheers, Greg On Feb 1, 2010, at 6:22 PM, zaxis wrote:

For me i like C style instead of layout. For example, func1 a = do -- ... a * 2 -- ...

I always write it as: func1 a = do { -- ...; a * 2; -- ...; }

However, i donot know how to write pure function using C style. func1 a = { -- ...; a * 2; -- ...; }

will not compile without `do`.

Sincerely!

----- fac n = foldr (*) 1 [1..n] -- View this message in context: http://old.nabble.com/About-code-style---tp27414627p27414627.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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