On Monday 26 September 2005 17:14, Rene de Visser wrote:
> Hello,
>
> I need to zip together multiple lists.
>
> The lists are sorted by date, and each entry in the list represents data
> for a time interval.
> The time intervals between the lists may be missmatched from each other.
Is this the sort of thing you want?
module Main where
data Event = Event { time :: Int, what :: String } deriving (Eq, Show)
zipToMaybes :: [Event] -> [Event] -> [(Maybe Event, Maybe Event)]
zipToMaybes [] [] = []
zipToMaybes [] (h:t) = ((Nothing, Just h):(zipToMaybes [] t))
zipToMaybes (h:t) [] = ((Just h, Nothing):(zipToMaybes t []))
zipToMaybes (ha:ta) (hb:tb)
| (time ha) == (time hb) = ((Just ha, Just hb):(zipToMaybes ta tb))
| (time ha) < (time hb) = ((Just ha, Nothing):(zipToMaybes ta
(hb:tb)))
| otherwise = ((Nothing, Just hb):(zipToMaybes (ha:ta)
tb))
main = interact $ const $ show $ zipToMaybes [Event 0 "Got up", Event 1 "Had
breakfast", Event 3 "Went to work"] [Event 0 "Got up", Event 2 "Went to
work"]
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