Function assoc

pub(crate) fn assoc<'ob>(
    key: &Rt<Slot<Gc<ObjectType<'ob>>>>,
    alist: &Rt<Slot<Gc<ListType<'ob>>>>,
    testfn: Option<&Rt<Slot<Gc<ObjectType<'_>>>>>,
    cx: &'ob mut Context<'_>,
    env: &mut Rt<Env<'_>>,
) -> Result<Gc<ObjectType<'ob>>>