[padator]

I think it's more related to Prolog than functions. In prolog you can use a predicate in many ways. For example append(L1, L2, L3) declared that the concatenation of the list L1 and L2 result in L3, but you can use it in a "reverse" way too (thx to Prolog awesomeness) like append(L1, L2, [1,2,3]) and Prolog will enumerate all possibilities for L1 and L2. This can be slow though, and I think 'mode' is a way to declare all this different way to use prediate (in, int, out), (out, out, in), etc. and maybe compile things efficiently. See https://www.mercurylang.org/information/doc-latest/mercury_r...