Showing Data.Ratio - different on GHC vs Hugs/Yhc
Hi Under Hugs and Yhc, showing a Ratio 1%2 gives "1 % 2". Under GHC showing 1%2 gives "1%2". Does the standard say anything about this? Is someone wrong? And how do Yhc/nhc/Hugs pass Bernouilli in the Nofib suite given that the output doesn't match? Thanks Neil
On Nov 16, 2007 2:12 PM, Neil Mitchell
Under Hugs and Yhc, showing a Ratio 1%2 gives "1 % 2". Under GHC showing 1%2 gives "1%2". Does the standard say anything about this? Is someone wrong? And how do Yhc/nhc/Hugs pass Bernouilli in the Nofib suite given that the output doesn't match?
Judging by the Read instance, the whitespace isn't considered significant.
Prelude Data.Ratio> map read ["1%2", "1 % 2", " 1 % 2 "] :: [Rational]
[1%2,1%2,1%2]
--
Dave Menendez
Neil Mitchell wrote:
Hi
Under Hugs and Yhc, showing a Ratio 1%2 gives "1 % 2". Under GHC showing 1%2 gives "1%2". Does the standard say anything about this? Is someone wrong?
Yes, ghc is wrong here, the Haskell 98 report [1] specifies: instance (Integral a) => Show (Ratio a) where showsPrec p (x:%y) = showParen (p > ratPrec) (showsPrec (ratPrec+1) x . showString " % " . showsPrec (ratPrec+1) y) While it doesn't really matter, it is a deviation from the standard. I would personally prefer it if rationals were shown as "1%2", because the space is not needed, and other show instances such as lists don't insert spaces either. [1]: http://haskell.org/onlinereport/ratio.html Twan
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David Menendez -
Neil Mitchell -
Twan van Laarhoven