[Haskell-cafe] Style

[Henning Thielemann]

On Fri, 24 Aug 2007, Mirko Rahn wrote:

>> tm = sum . takeWhile(>0) . iterate f . f
>>    where f = flip div 5
>
> Quite nice. I like
>
> tm5 0 = 0
> tm5 n = let q = div n 5 in q + tm5 q
>
> This version corresponds to what I'm think when parsing |tm|, so I wrote it 
> down directly.

Since the original poster used the message title "style", I want to 
mention that his solution is good style, because it keeps logical steps 
separated, and thus lets you inspect meaningful interim results.
  (iterate f . f) computes the number of natural numbers up to n with 
factors 5, 5^2, 5^3 and so on. Then you like to sum these up (sum), but 
before this, you must limit the list to a reasonable finite prefix 
(takeWhile (>0)). Of course, using 'show' and counting the zeros is more 
intuitive. It is not efficient, but it will serve as a nice test of 'tm's 
correctness.