Floating point problems

David Roundy droundy at darcs.net
Thu Aug 31 14:55:52 EDT 2006

On Wed, Aug 30, 2006 at 06:04:47PM -0400, Lennart Augustsson wrote:
> On Aug 30, 2006, at 14:58 , David Roundy wrote:
> >The trouble here is that ghci is printing more digits than it
> >really ought to be printing.
> No, I don't think it is.  Ghci is printing the number that is closest  
> of all numbers in decimal notation to the Double in question (i.e.,  
> 0.1+0.2).  Printing it with fewer decimals would yield a different  
> number if it was read back.

Then I guess the problem is that the output of show isn't appropriate
for human interaction? In many cases it's nice for (read . show) to be
identity, but I don't prefer this for floating point numbers.  If I
want a bitwise accurate output of a Double, I'll dump a binary.  When
I output decimal, I generally want something friendly to the human
who's reading it, which to me means outputting only significant
digits (which is admittedly an ill-defined concept).
David Roundy

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