foldr is supposed to start folding from the right side (as the name suggests).

and this is why it is synonymous to "list construction" as I'm told

for e.g:

> foldr (:) [ ] [1,2,3,4,5]

[1,2,3,4,5]

In the same spirit I'm trying to construct a Foldable instance of my own type:

data Li a = Nil | Cons a (Li a)

    deriving (Show)

instance Foldable Li where

    foldr f b Nil = b

    foldr f b (Cons a y) = foldr f (f a b) y

So I'm trying out foldr for my type:

> foldr Cons Nil (Cons 1 (Cons 2 Nil))

Cons 2 (Cons 1 Nil)

This shows my foldr implementation i'm not folding from right side, 

but how can I possibly do that - the data could have been an infinite stream.

It feels like I will never be able to truly write a foldr implementation with "right" folding mechanism.

Any thoughts?

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