Why Not Rust?(matklad.github.io)

    trait Prop<'a, T> {
        fn p<F: Fn(&'a T) -> bool>(f: F) -> Self;
        fn eval(&self, &'a T) -> bool;
    }

    enum LiftedBool<'a, T, F: Fn(&'a T) -> bool> {
        Base(Box<F>),
        And(LiftedBool<'a, T, F>, LiftedBool<'a, T, F>),
        Or(LiftedBool<'a, T, F>, LiftedBool<'a, T, F>),
        Not(LiftedBool<'a, T, F>),
    }

    impl<'a, T, F: Fn(&'a T) -> bool> Prop<'a, T> for LiftedBool<'a, T, F> {
        fn p<F: Fn(&'a T) -> bool>(f: F) -> Self {
            // this fails because `F` in the impl doesn't necessarily unify with `F` in the trait definition
            // it can be made to work with `dyn` for the function argument but requires boilerplate to actually use
        }

        fn eval(&self, &'a T) -> bool {
            // obvious evaluation by cases
        }
    }

    containsVal = false
    for _,i := range array {
        if (i == val) {
            containsVal = true
        }
    }