On Aug 30, 2006, at 14:58 , David Roundy wrote:
On Wed, Aug 30, 2006 at 07:38:35PM +0100, Jamie Brandon wrote:
I recently defied my supervisor and used Haskell to write my
coursework instead of C. All went well until I needed floating point
and started having odd results. As far as I can tell it isn't
substantially affecting my results but it is rather embarrassing
after slagging off C so much. Here are some examples:
*Main> 0.2 + 0.1
0.30000000000000004
*Main> 0.200000000000000 + 0.100000000000000000
0.30000000000000004
*Main> 0.3 + 0.1
0.4
*Main> 0.2 + 0.1
0.30000000000000004
*Main> it + 0.1
0.4
I assume this is a result of the discrepancy between binary and
decimal
representations of the numbers. Is there any way around? For a
start, it
would be nice to have a simple way to get 0.1 + 0.2 == 0.3 = True
This is with GHC 6.4.1 and GCC 4.0.3
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.
-- Lennart
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