Re: [Haskell-cafe] Thompson's Exercise 9.13

10 Apr 2005


      Am Sonntag, 10. April 2005 19:46 schrieb Daniel Fischer:
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so it doesn't work in all cases. The idea is nice, though:
import Data.Maybe
finit  = catMaybes . foldr f [Nothing] . map Just
  where
  f x ys = case ys of
                    [Nothing] -> []
                    _             -> x:ys
will do fine.
Ooooops, only for nonempty lists!
Replace catMaybes with 'map (maybe (error "init of []") id)'
and it'll work also for empty lists.