newtypes always turn into no code. The UNPACK is therefore asking to unpack the Integer inside a Day, and that we can't do because Integer has more than one data constructor. Ditto Pico. So just drop the UNPACKS. Keep the ! though, to keep it strict
S From: [email protected] [mailto:[email protected]] On Behalf Of Eugene Kirpichov Sent: 28 October 2011 10:41 To: Haskell Cafe Subject: [Haskell-cafe] When does the UNPACK pragma work? Hi, I'm trying to speed up Data.Time (the time package) 'cause my program is spending a very substantial fraction of time manipulating dates. I decided to start with strictifying and unpacking the date/time types, as there's no point in having them be lazy and I indeed had a lot of allocation in date/time arithmetic in my performance profile. data UTCTime = UTCTime { utctDay :: {-# UNPACK #-} !Day, utctDayTime :: {-# UNPACK #-} !DiffTime } (unpacks and strictness mine) newtype Day = ModifiedJulianDay {toModifiedJulianDay :: Integer} newtype DiffTime = MkDiffTime Pico And Pico is also essentially a newtype for Integer. So, I'm getting warnings on this definition of UTCTime. QUESTION: Is it the case that I can only UNPACK primitive fields, and not even their newtypes? Data\Time\Clock\UTC.hs:30:16: Warning: Ignoring unusable UNPACK pragma on the first argument of `UTCTime' In the definition of data constructor `UTCTime' In the data type declaration for `UTCTime' Data\Time\Clock\UTC.hs:30:16: Warning: Ignoring unusable UNPACK pragma on the second argument of `UTCTime' In the definition of data constructor `UTCTime' In the data type declaration for `UTCTime' -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/
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