[Haskell-cafe] 'Associative' order of calling

Matteo Acerbi matteo.acerbi at gmail.com
Sat Oct 24 18:23:51 UTC 2015

On Sat, Oct 24, 2015 at 8:12 PM, Janis Voigtländer <
janis.voigtlaender at gmail.com> wrote:

> It has already been established in this thread what Charles meant by 3.
> He meant that a fold-function that has the property he is after would
> guarantee that it:
> a) takes all the content elements from a data structure, say x1,...,xn,
> b) builds an application tree with the to-be-folded, binary operation f in
> the internal nodes of a binary tree, whose leafs, read from left to right,
> form exactly the sequence x1,...,xn,
> c) evaluates that application tree.
> Do you agree that what I describe above is a property of a given fold-like
> function, not of the f handed to that fold-like function?

I might lack some basic knowledge, so thanks for asking.

What does it mean to take all the content elements from a data structure?

If one has f a = Bool -> a, and a value

xs :: f Int
xs True  = 2
xs False = 3

what are x1 and x2?


PS. I won't be able to read the answer before tomorrow. :-)
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