filter

In std/collections.

elementwise fn filter<F<_> : Iterable<_>, T, U>(self: F<T>, by: T -> Is<U>) : F<U>
elementwise fn filter<T, U>(self: Option<T>, by: T -> Is<U>) : Option<U>

The elements for which a type test holds, each at the tested type. A by of type T -> Is<U>, such as x => x | is(Int), makes the result an F<U>. Over an Option<T>, the result is the value when it is present and the test holds, and none otherwise.

elementwise fn filter<S : Iterable<T>, T>(self: S, by: T -> Bool) : S
elementwise fn filter<T>(self: Option<T>, by: T -> Bool) : Option<T>

The elements for which by is true, in their order, in a collection of the input's type. Over an Option<T>, the result is the value when it is present and by holds, and none otherwise.