Question

Given the following example

foldr(\ x y -> ........

if the input is a list for example [1,2,3]

what is x and what is y?

Answer 1

Let’s take a look at the type for foldr.

foldr :: (a -> b -> b) -> b -> [a] -> b

Since you’re providing the function that uses x and y, you can see from the type that x will be a value from your list ([1,2,3]), and y must be the accumulator value, which you initialize with the second parameter to foldr.