On Sat, 03 Jul 2010 12:48:56 -0700, Dan Doel <dan.d...@gmail.com> wrote:
Then the instance declares infinitely many instances C Bool a a. This is a
violation of the fundep. Based on your error message, it looks like it ends up
treating the instance as the first concrete 'a' it comes across, but who
knows?
Hmmm.. it doesn't look like a first concrete lockdown. The following works
fine:
opres1 :: Int -> Int
opres1 = op True
opres2 :: String -> String
opres2 = op True
main = do putStrLn $ op True "start"
putStrLn $ show $ opres1 5
putStrLn $ opres2 $ opres2 $ show $ opres1 6
putStrLn $ opres2 "done"
As a side note, although I agree it abuses the fundeps intent, it was handy for the
specific purpose I was implementing to have a "no-op/passthrough" instance of
op. In general I like the typedef approach better, but it looks like I must sacrifice
the no-op to make that switch.
--
-KQ
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