[Haskell-cafe] Shouldn't this be lazy???

[Henning Thielemann]

On Fri, 22 Jun 2007, Olivier Boudry wrote:

> -- | create sections from tag type and attribute
> getSectionsByTypeAndAttr :: String -> (String, String) -> String -> IO [[Tag]]
> getSectionsByTypeAndAttr tagType attr url = do
>     tags <- unsafeInterleaveIO $ liftM parseTags $ openURL $ url
>     (return . filterByTypeAndAttr tagType attr) tags
>   where
>     filterByTypeAndAttr :: String -> (String, String) -> [Tag] -> [[Tag]]
>     filterByTypeAndAttr t a = sections (~== TagOpen t [a])

I think if openURL is not lazy, then the unsafeInterleaveIO will not help
much because it only defers the whole computation until the first part of
the result is requested. One call to unsafeInterleaveIO cannot divide a
big IO action into small pieces of lazily triggered actions. I think
unsafeInterleaveIO is unnecessary here.