[Haskell-cafe] Re: Would you mind explain such a code ?

I know myFoldl implements foldl using foldr. However i really donot know how it can do it ?

You will probably like Graham Hutton A Tutorial on the Universality and Expressiveness of Fold JFP, 1999. http://www.cs.nott.ac.uk/~gmh/fold.pdf Section 5.1 (actually, suml in Section 5) of the paper explains how the expression of foldl in terms of foldr can be _calculated_. The result is correct by construction.