Efficient implementation of deeply nested lists

[Kay Schluehr]

I want to manipulate a deeply nested list in a generic way at a
determined place. Given a sequence of constant objects a1, a2, ..., aN
and a variable x. Now construct a list from them recursively:

L = [a1, [a2, [....[aN, [x]]...]]

The value of x is the only one to be changed. With each value of x a
new instance of L is needed so that we actually have a function:

L = lambda x: [a1, [a2, [....[aN, [x]]...]]

I'm seeking for an efficient implementation that does not recompute the
whole list each time. Any ideas?

Kay