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

[oleg at okmij.org]

> 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.