The Term trait

The ATerm trait represents a first-order term in the ATerm library. It provides methods to manipulate and access the term's properties.

pub trait Term<'a, 'b>
where
    'b: 'a,
{
    /// Functions taking 'b for self and return a reference with lifetime 'a.
    fn function(&'b self) -> ATermRef<'a>;
}

This trait is rather complicated with two lifetimes, but this is used to support both the ATerm, which has no lifetimes, and ATermRef<'a> whose lifetime is bound by 'a. Because now we can be require that 'b: 'a for the implementation of Term<'a, 'b> for ATerm, we can safely return ATermRef<'a> from methods of Term<'a, 'b>. Without the 'b: 'a` constraint, we would implement Term<'a> for ATerm, for all lifetimes 'a, including the 'static lifetime, and this would be unsound. Alternatively, we could have implemented Term<'a> for &'a ATerm, but then ATerm cannot be used directly as a Term in many places.