`Contains` behavior is confusing

[epage]

Currently, the expression hash.contains(5) gets translated to contains(hash).eval(&5). If you understand that context, it makes sense. If you are coming from another language that uses in or contains operators, it gets confusing (the expression 4 < 5 gets translated to: lt(5).eval(&4))

• Some languages have an in operator. So 5 in hash would naturally translate to in(hash).eval(&5).
• Some languages flip that and have a contains operator. So hash contains 5 would naturally translate to contains(5).eval(&hash).

[epage]

My main interest is I'd like a predicate that is the opposite of the current contains and would like names that help clarify the intent between the two.

[epage]

On the flip side, hamcrest uses contains for comparing two iterables, weird.

assert_that!(&vec!(1i, 2, 3), contains(vec!(1i, 2)));
assert_that!(&vec!(1i, 2, 3), not(contains(vec!(4i))));

assert_that!(&vec!(1i, 2, 3), contains(vec!(1i, 2, 3)).exactly());
assert_that!(&vec!(1i, 2, 3), not(contains(vec!(1i, 2)).exactly()));

assert_that!(&vec!(1i, 2, 3), contains(vec!(1i, 2)).in_order());
assert_that!(&vec!(1i, 2, 3), not(contains(vec!(1i, 3)).in_order()));

https://github.com/ujh/hamcrest-rust

I'd like to also have iterable predicates but I assume set terminology would be best