[Haskell-cafe] Re: Write Haskell as fast as C.

[Dan Weston]

Dan Weston wrote:
> Ketil Malde wrote:
>>> mkAnn :: ByteString -> Annotation
>>> mkAnn = pick . B.words
>>>     where pick (_db:up:rest) = pick' up $ getGo rest
>>>           pick' up' (go:_:ev:_) = Ann (B.copy up') (read $ B.unpack 
>>> go) (read $ B.unpack ev)
>>>           getGo = dropWhile (not . B.isPrefixOf (pack "GO:"))
> 
> It seems at first face miraculously coincidental that the dropWhile in 
> the getGo definition knows to stop dropping when there are exactly 4 
> elements, in order to match the pattern in the second parameter of the 
> pick' definition, whose argument is provided by (getGo Rest).
> 
> What magic makes this true? Just curious...

I didn't mean "exactly 4", but "at least 3". Otherwise, I'm still 
curious! :)