[Haskell-cafe] I need help getting started

[John Bender]

Mitchell

You might also be interested in the beginners mailing list. I've been
enjoying for about a month now!

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

> On Sat, Apr 24, 2010 at 10:34 PM,  <mitchell at 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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