I'm learning Haskell and I found an interesting implementation of init using foldr. However I have difficulty understand how it works. 

Consider I have a input of [1,2,3], then is would become

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

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.