[Haskell-cafe] Re: Is logBase right?

Henning Thielemann lemming at henning-thielemann.de
Tue Aug 25 09:20:23 EDT 2009

On Sun, 23 Aug 2009, Lennart Augustsson wrote:

> You're absolutely right.  It would be easy to change logBase to have
> special cases for, say, base 2 and base 10, and call the C library
> functions for those.  In fact, I think it's a worth while change,
> since it's easy and get's better results for some cases.

I think, the current implementation should left as it is. For fractional 
bases, no one would easily detect such imprecise results and report them 
as problem. So, it seems like people need a logarithm of integers, so they 
should be supplied with a special logarithm function for integers. For the 
other use cases, where 10 as base is one choice amongst a continuous set 
of rational numbers it would not be a problem to give the imprecise 
result. In the general case I would not accept a speed loss due to a check 
against 2 and 10 as base.

In dynamically typed languages like Python this might be different, 
because their users might not care much about types. It may not be 
important for them, whether a number is an integer or a floating point 
number that is accidentally integral. However, Python distinguishes 
between these two kinds of integers, but only dynamically.

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