On Wed, 11 Mar 2009, R J wrote:
foldl and foldr are defined as follows:
foldr :: (a -> b -> b) -> b -> [a] -> b
foldr f e [] = e
foldr f e (x : xs) = f x (foldr f e xs)
foldl :: (b -> a -> b) -> b -> [a] -> b
foldl f e [] = e
foldl f e (x : xs) = foldl f (f e x) xs
1. I understand how these definitions work, and yet I'm unable to implement
foldl in terms
of foldr. What's a systematic approach to identifying such an implementation,
and what is
the implementation?
You are lucky, I recently wrote
http://haskell.org/haskellwiki/Foldl_as_foldr
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