Lambda is easy to reason about, since it is guaranteed to not have any side effects. To juggle the other kinds of expressions like this you'd need a more elabor

Lambda is easy to reason about, since it is guaranteed to not have any side effects. To juggle the other kinds of expressions like this you'd need a more elaborate purity analysis. So, lambda is a very easy prey for the DCE. Also, there are some specific optimisations, like beta-reduction and closure inlining.