Dear all, https://github.com/nushio3/practice/blob/master/recursion-schemes/FibTest.hs
After learning fix-point operators, I found an answer by myself. ``` fibBase :: (Integer -> Integer) -> Integer -> Integer fibBase fib n | n <= 1 = 1 | otherwise = fib (n-1) + fib (n-2) fibWithFix :: Integer -> Integer fibWithFix = fix fibBase ``` I can say `fibBase` is free of recursion, despite the facts that apparently it uses a name `fib` on RHS which it binds on the LHS, and that the entire structure seems very similar to the recursive version of `fib` . 2013/6/16 Takayuki Muranushi <muranu...@gmail.com> > In an attempt to understand why cata- and anamorphisms are considered so > important, I found multiple implications that you can write any recursive > functions in terms of nonrecursive functions and ana, cata (am I right > here?) so I'm trying to practice the rewrite by a few functions. I'm > following a recipe found here: > > http://lambda-the-ultimate.org/node/4290 > > ~~~ > Given a function that recurses on itself, do a partial CPS transform so > that it only ever recurses on itself with tail calls. Then, convert the > recursive calls to codata returns, so that the function either returns > TheAnswer or StillWorking with enough parameters to describe the recursive > call / continuation state. This codata can be built with an unfold and can > be collapsed back down to the final answer with a fold. > ~~~ > > > https://github.com/nushio3/practice/blob/master/lens/banana/CollatzTest.hs > https://github.com/nushio3/practice/blob/master/lens/banana/FibTest.hs > > I find it difficult to understand the terminology, and the above attempts > are only halfway done. I guess ( TheAnswer or StillWorking ) structure is > the one found in iteratee/enumeratee. But I don't know how to "build a > codata with unfold." > > I'd appreciate any advice. > > Best, > > -- > Takayuki MURANUSHI > The Hakubi Center for Advanced Research, Kyoto University > http://www.hakubi.kyoto-u.ac.jp/02_mem/h22/muranushi.html > -- Takayuki MURANUSHI The Hakubi Center for Advanced Research, Kyoto University http://www.hakubi.kyoto-u.ac.jp/02_mem/h22/muranushi.html
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