[Haskell-cafe] Define variable types

[Miguel Mitrofanov]

Note also that Helium ISN'T Haskell; it lacks hell of a lot of Haskell98 features (not to mention common extensions).

05.02.09, 14:57, "Roman Cheplyaka" <roma at ro-che.info>:

> * Tsunkiet Man <temp.tsun at gmail.com> [2009-02-05 12:37:22+0100]
> > Hello,
> > 
> > I'm new to Haskell and it seems like a very nice language to learn. However
> > I'm not really familiar with the errormessages it produces. I am using a
> > Helium interpreter. I've created the following module (however it is just a
> > small sketch). I've written the following code:
> > 
> > fac :: Int -> Int
> > fac n = product[1..n]
> > 
> > boven :: Int -> Int -> Int
> > boven n k = (fac n) `div` fac k * fac (n-k)
> > 
> > bin :: Int -> Int -> Int -> Int
> > bin n k p   |(n-k)>0 && k>0 = (boven n k) * (p^k) * (1-p)^(n-k)
> >             |(n-k)<0 && k>0 = (boven n k) * (p^k) * (1/((1-p)^(-(n-k))))
> >             |(n-k)<0 && k<0 = (boven n k) * (1/(p^(-k))) *
> > (1/((1-p)^(-(n-k))))
> > 
> > When I load this into my interpreter it says:
> > 
> > Compiling ./Test.hs
> > (11,55): Type error in infix application
> >  expression       : 1 / ((1 - p) ^ (-(n - k)))
> >  operator         : /
> >    type           : Float -> Float -> Float
> >    does not match : Int   -> Int   -> Int
> > (12,47): Type error in infix application
> >  expression       : 1 / (p ^ (-k))
> >  operator         : /
> >    type           : Float -> Float -> Float
> >    does not match : Int   -> Int   -> a
> > (12,62): Type error in infix application
> >  expression       : 1 / ((1 - p) ^ (-(n - k)))
> >  operator         : /
> >    type           : Float -> Float -> Float
> >    does not match : Int   -> Int   -> a
> You can't use fractional division (/) with integers. You can convert
> integers to fractions using fromIntegral. E.g.:
>     1 / fromIntegral ((1 - p) ^ (-(n - k)))
> (literals like 1 doesn't need to be converted because they are
> polymorphic)
> -- 
> Roman I. Cheplyaka :: http://ro-che.info/
> "Don't let school get in the way of your education." - Mark Twain
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