Checking if all elements are equal with map/fold

Given a list of elements, like [1, 1, 1] or ["a", "a", "a"], how can I check if they're all equal using map/fold?

I tried to do something like this:

let eq lst = fold (=) lst

which doesn't compile because there's no accumulator, but I'm really not so sure what to put for the accumulator. Any help is appreciated.