[Haskell-beginners] Re: question about styles of recursion
bbxx789_05ss at yahoo.com
Thu Mar 26 16:43:24 EDT 2009
Michael Mossey <mpm <at> alumni.caltech.edu> writes:
> In RWH, in the exercises at the end of the book,
There are no exercises at the end of the book.
> I was told to write a
> function that averages the integer values in a list. I wanted to do this
> using on the tools we had been presented, which did not include
Ok. That sounds like you are working on the exercises for chapter 3
on p.69, specifically exercise 3. The length function was introduced
before the sum function, which I see you are using in your
function definition. See p. 15. The length function was also
mentioned in exercise 1, and the instructions for exercise 3 mention
using the length of the list.
> So I thought of writing a recursive function in which each
> case passes an accumulator of the "sum so far" as well as a count of
> node "up to the point", and the base case does the actual division. I
> was wondering if there is a better way of doing it (using the just ideas
> up to chapter 3, so no length, no higher order functions, no foldr/foldl
> or map).
> myAvg' :: Int -> [Int] -> [ Double ] -> Double
> myAvg' sum count  = sum / fromIntegral count
> myAvg' sum count (x:xs) = myAvg' (x + sum) (n + 1) xs
Use variables that are defined?
Prelude Data.List> :load ehask.hs
[1 of 1] Compiling Main ( ehask.hs, interpreted )
ehask.hs:3:44: Not in scope: `n'
Failed, modules loaded: none.
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