Noticed this today: ghci> let xs = [0.0,0.1 .. 86400.0] in maximum xs 86400.0000005062
enumFromThenTo is implemented by numericEnumFromThenTo: https://github.com/ghc/ghc/blob/a90085bd45239fffd65c01c24752a9bbcef346f1/libraries/base/GHC/Real.hs#L227 Which probably accumulates error in numericEnumFromThen with the (m+m-n): numericEnumFromThen n m = n `seq` m `seq` (n : numericEnumFromThen m (m+m-n)) Why not define numericEnumFromThen as: numericEnumFromThen n m = let d = m - n in d `seq` go d n where go delta x = x `seq` (x : go delta (x + delta)) (or with BangPatterns) numericEnumFromThen n m = go (m - n) n where go !delta !x = x : go delta (x + delta) Seems like we'd save a lot of subtractions by using the worker function. _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
