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| author | Brian McKenna <brian@brianmckenna.org> | 2014-12-02 17:53:38 +0100 |
|---|---|---|
| committer | Herbert Valerio Riedel <hvr@gnu.org> | 2014-12-02 17:54:50 +0100 |
| commit | 7c38e985aa211ca44039c6d1db9fa13690749c59 (patch) | |
| tree | 1c97a63cd1e023644bc97c8144ed348dab6dffb9 /packages | |
| parent | 6b063ef2a1f68290b51778a38e9b89b6fec5e170 (diff) | |
| download | haskell-7c38e985aa211ca44039c6d1db9fa13690749c59.tar.gz | |
Make `read . show = id` for Data.Fixed (fix #9240)
The QuickCheck property now succeeds:
prop :: Fixed B7 -> Bool
prop a = read (show a) == a
This changes the Show instance for Fixed to round up, rather than down
when calculating a digit. This needs to happen because Read also
rounds down:
data B7
instance HasResolution B7 where
resolution _ = 128
1 / 128 = 0.0078125
read "0.007" = (0.000 :: Fixed B7)
Here is an example of the change to Show:
showFixed False (0.009 :: Fixed B7)
-- Broken: "0.007"
-- Fixed: "0.008"
And now Read can continue to round down:
read "0.008" = (0.0078125 :: Fixed B7)
Reviewed By: hvr, ekmett
Differential Revision: https://phabricator.haskell.org/D547
Diffstat (limited to 'packages')
0 files changed, 0 insertions, 0 deletions