What about these?

    f1 list =  foldr (&&) True list    -- && is logical and
    f2 list = foldr (||) False list    -- || is logical or
    f3 list =  foldl max (head list) (tail list)
    f4 list =  foldl min (head list) (tail list)

Do you consider them trivial, or too hard to understand without rewriting as a loop? Honest question.

I think if you use a non-associative function as an argument, then fold is hard to understand. But then an explicit loop won't help much.

Trivial, they're in the same category with add and multiply.

Check out http://lambda-the-ultimate.org/node/587 for some non trivial examples.

Coincidentally, I've always found finding the maximum or minimum of a list with a for loop really finicky. It's much easier with a fold.

I know exactly what you mean. The fact is, every single program you write is going to be executed by a little stateful machine ticking along. So if your programming language doesn't model such a machine and instead uses higher-order constructs, then I will have to mentally translate everything you write to make full sense of it.

> then I will have to mentally translate everything you write to make full sense of it.

But why? A SQL query or a Java/Python/whatever program might get translated to zillions of CMP and JMP instructions, but I see no reason why you should have to do that translation yourself in order to read the code. In fact that would practically preclude the use of any minimally high-level programming language.

I believe that was the GP's point, he just omitted the sarcasm tags ;)