On Sat, Apr 24, 2010 at 9:57 PM, Luke Palmer <lrpalmer@gmail.com> wrote:

On Sat, Apr 24, 2010 at 10:34 PM, <mitchell@kaplan2.com> wrote:
> Hi,
>
>
>
> I’m just starting to learn, or trying to learn Haskell. I want to write a
> function to tell me if a number’s prime. This is what I’ve got:
>
>
>
> f x n y = if n>=y
>
>           then True
>
>           else
>
>           if gcd x n == 1
>
>           then f x (n+1) y
>
>           else False
>
>
>
>
>
> primeQ x = f x 2 y
>
> where y = floor(sqrt(x))

Pretty good so far. The only trouble is that the type of x is
inconsistent. In f it is an integer, but in primeQ it is a floating
point (because you are taking its square root). Getting past this
just involves understanding Haskell's type system peculiarities.
Change that last line to:

where y = floor (sqrt (fromIntegral x))

And you should be fine. (Untested)

In the future, post the error that you are getting addition to the
code that is causing it. That helps us find it faster.

Luke

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