[Haskell-cafe] Mystery of an Eq instance

[Tom Ellis]

On Fri, Sep 20, 2013 at 09:47:24PM +0530, damodar kulkarni wrote:
> Ok, let's say it is the effect of truncation. But then how do you explain
> this?
> 
> Prelude> sqrt 10.0 == 3.1622776601683795
> True
> Prelude> sqrt 10.0 == 3.1622776601683796
> True
> 
> Here, the last digit **within the same precision range** in the fractional
> part is different in the two cases (5 in the first case and 6 in the second
> case) and still I am getting **True** in both cases.

What do you mean the "same precision range"?  Notice:

    Prelude> 3.1622776601683795 == 3.1622776601683796
    True
    Prelude> 3.1622776601683795 == 3.1622776601683797
    True
    Prelude> 3.1622776601683795 == 3.1622776601683798
    False

The truncation happens base 2, not base 10.  Is that what's confusing you?

Tom