MicrosoftI've been reading the other comments and thoughts on this, and the 80/20 rule is coming to mind (or perhaps 95/5).
LAMBDAs, and to some extent LET, fill the gap between using existing Excel formulas (and some spreadsheet real-estate) and creating full-blown UDFs using an add-in methodology (vba module, .xla, .xll etc). They allow encapsulation and re-use of the formula logic in a quick lightweight way, and are more portable. But just how big is that gap?
My three-pennies' worth is that if you could just improve the co-ordination with Name Manager by tying the process into the usual UDF registration (eg the arguments to the xlfRegister C-API call): take the names of the parameters in the LAMBDA as the text for the parameter names in the Register function, and the Name comment as the function description. It would also be nice for the formula to appear in the Function Wizard list (under "user-defined"). OK, so you don't get the optional parameter description text, but that's not really the end of the world.
I think this would neaten up the LAMBDA implementation and increase its usability by making the LAMBDA functions fit better with users' existing experience of functions. Maybe all the "good stuff" like debugging, formula builders, extending the Name object in the Object Model, modifying the Name Manager display (tab for LAMBDAs?) etc can come in LAMBDA 2.0?
(While I am here ... maybe also fix the namespace issue with VBA UDFs: I declare Function MoreAdding() in VBA, it appears in the Function Wizard as MoreAdding (and in the formula completion when typing in the cell), but the cell's formula is =moreadding(), ie losing the capitalization. It's just annoying to a pedant like me!)
