3 ms·

I have never seen a non-trivial example of fold* (i.e. anything other than "+" or "*") that I didn't have to spend several seconds or minutes rewriting it (ment

I have never seen a non-trivial example of fold* (i.e. anything other than "+" or "*") that I didn't have to spend several seconds or minutes rewriting it (mentally or in typing) as a loop to figure out WTH it is doing.

sirclueless 15y ago
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.
- nandemo 15y ago
  > 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.
  - reinhardt 15y ago
    I believe that was the GP's point, he just omitted the sarcasm tags ;)
nandemo 15y ago
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.
- tikhonj 15y ago
  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.
- reinhardt 15y ago
  Trivial, they're in the same category with add and multiply. Check out http://lambda-the-ultimate.org/node/587 http://lambda-the-ultimate.org/node/587 for some non trivial examples.

sirclueless 15y ago

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.

nandemo 15y ago
> 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.
- reinhardt 15y ago
  I believe that was the GP's point, he just omitted the sarcasm tags ;)

nandemo 15y ago

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.

tikhonj 15y ago
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.
reinhardt 15y ago
Trivial, they're in the same category with add and multiply. Check out http://lambda-the-ultimate.org/node/587 http://lambda-the-ultimate.org/node/587 for some non trivial examples.