[Haskell-cafe] A systematic method for deriving a defintion of foldl using foldr?

[Max Rabkin]

2009/3/11 R J <rj248842 at hotmail.com>:
> 2.  I believe that the reverse implementation--namely, implementing foldr in
> terms of foldl--is impossible.  What's the proof of that?

That's correct. Consider their behaviour on infinite lists.

--Max