foldLeft v. foldRight - does it matter?

Question

Previously, Nicolas Rinaudo answered my question on Scala\'s List foldRight Always Using foldLeft?

Studying Haskell currently, my understanding is that foldRig

Answer 1

I'm no Scala expert, but in Haskell, one of the most important differentiating features between foldl' (which really should be the default left fold) and foldr is that foldr will work on infinite data structures, where foldl' will hang indefinitely.

In order to understand why this is, I recommend visiting foldl.com and foldr.com, expanding the evaluations a couple of times, and reconstructing the call tree. You'll quickly see where foldr is appropriate versus foldl'.