Announcing LAMBDA: Turn Excel formulas into custom functions (techcommunity.microsoft.com)

With Turing-completeness, the obvious problem is infinite recursion.

Say, you defined a function OMEGA as:

        =LAMBDA(F, F(F))

and then call

        =OMEGA(OMEGA)

hmm.

Well, it is not clear if Excel's LAMBDAs are first-class or not. If not, the above wouldn't work.