Hi folks, sorry for multiple copies of this email, but my mailserver had a problem and thought I am sending spam which is hopefully not true. Since I got a replay allready I modified my mail a bit.
I was wondering why we don't have an annotation or pragma for function to tell
the compiler that we _need_ this particular recursive function to be unfolded.
If the compiler cannot do this for some reason it should produce an error
message to help you modifying your code. I have regularly problems that my
code is either not strict enough or my functions are not unfolded. I find it
annoying that this is a regular show stopper and consumes much time to fix.
Here is an example: a search function for strings, which should return the
index and the rest of the string after the first occurrence: search0 will not
be unfolded by ghc -O even with {#- INLINE search0 -#} (I don't know why, it
looks tail-recursive to me)
whereas search1 is just fine.
search0 :: Int -> String -> String -> (String, Int)
search0 i [] _ = ([],i)
search0 i haystack needle =
let len = length needle
in if isPrefixOf needle haystack then (drop len haystack, i+len)
else search0 (seq i (i+1)) (drop 1 haystack) needle
search1 :: Int -> String -> String -> (String, Int)
search1 i [] _ = ([],i)
search1 i haystack needle =
let i = elemIndex True $ map (isPrefixOf needle) $ tails haystack
len = length needle
in case i of
Just index -> (drop (index+len) haystack, index + len)
Nothing -> ([],0)
Regards!
Georg
--
---- Georg Martius, Tel: +49 177 6413311 -----
------- http://www.flexman.homeip.net ----------
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