I personally don't think it's worth the minor conceptual simplification to treat LET forms as lambdas, but YMMV. It's only slightly more complicated to handle both LET forms and LAMBDA forms as things that can introduce values into the compile-time environment, but substantially more complicated to do the unboxing and inlining you'd have to do to ensure that the common case of defining a bunch of local variables that are not closed over does not end up consing or performing a function call.