Hello! I'm learning Haskell and I found an interesting implementation of init using foldr. However I have difficulty understand how it works. *init' xs = foldr f (const []) xs id* * where f x g h = h $ g (x:)* Consider I have a input of *[1,2,3]*, then is would become *f 1 (f 2 ( f 3 (const []))) id* I substitute those parameters into f and the innermost one becomes *h $ (const []) (1:)*, which is simply *h []*. However when I want to reduce the expression further, I found it's hard to grasp. The next one becomes *f 2 (h [])* , which is *h $ (h []) (2:)* if it works like that. This looks confusing to me. To match the type of *foldr*, h should be of type *[a] -> [a]* and *h []* would just be of type *[a]*, which isn't applicable to *(2:)*. I also thought it in another way that *f x g* returns a function of type *([a] -> [a]) -> [a],* this kinda makes sense considering applying *id* afterwards. But then I realized I still don't know what this *h* is doing here. It looks like *h* conveys *g (x:)* from last time into the next application. Did I miss something when I think about doing fold with function as accumulator? I'd really appreciate if anyone could help me with this.