Whats wrong with my if?

So I just started learning haskell and I'm trying to use this if statement:

[if (((mod x 3) == 0) && ((mod x 5) == 0)) then "Fizzbuzz" else x | x <- [1..50]]

but when I compile in ghci I get the following error:

No instance for (Integral [Char])
      arising from a use of `mod' at baby.hs:22:19-25
    Possible fix: add an instance declaration for (Integral [Char])
    In the first argument of `(==)', namely `(mod x 3)'
    In the first argument of `(&&)', namely `((mod x 3) == 0)'
    In the expression: (((mod x 3) == 0) && ((mod x 5) == 0))
Failed, modules loaded: none.

Ok, so I've figured out that x is inferred to be a string because the if is returning an explicit string, therefore this entire function wouldn't work. S开发者_开发技巧o how would I actually solve this problem? (I know my question is dumb, but I'm not used to ether the functional paradigm or having static typing with type inference).

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The 'then' and 'else' branches must have the same type. "Fizzbuzz" is a string where-as x is an Int. If you're just going to print the result then just put show x for your else branch.

Perhaps this would be good to add to the if/then/else section of Haskell's common misunderstandings. For the same reason the else branch must exist, it also must have the same type as the then.

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The problem is not in this part of the code. The error message is about the type of mod being mod :: (Integral a) => a -> a -> a, but x supposedly being of type [Char].

I am guessing that the type of x is being inferred here (since the type should be Int). Therefor in order to debug the problem I suggest you declare the type of your functions, like this:

f :: Int -> ...
f x ... = if (((mod x 3) == 0) && ((mod x 5) == 0))...

If you still have a problem, post the rest of the code.

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All you really have to do is add show in order to convert your Int into a String.

[if mod x 3 == 0 && mod x 5 == 0 then "Fizzbuzz" else show x | x <- [1..50]]

wich in turn can be written as:

map (\x -> if mod x 15 == 0 then "Fizzbuzz" else show x) [1..50]

---

main = mapM_ (putStrLn . fb) [1..100]

fb :: Int -> String
fb x | [3,5] `divides` x = "fizzbuzz"
     |   [5] `divides` x = "buzz"
     |   [3] `divides` x = "fizz"
     | otherwise         = show x

divides :: [Int] -> Int -> Bool
xs `divides` y = y `mod` product xs == 0

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From the looks of it, you are trying to solve ProjectEuler's problem 1. Try to use the "mod" function in its infix form, i.e. like this :

if ((x `mod` 3 == 0) && (x `mod` 5 == 0)) then blah blah

I think this will force the compiler to think that x is going to be an Int. Otherwise, you'll have to provide us with more info, like KennyTM, luqui and TomMD proposed (maybe the error is somewhere else down the line)!