Forum Discussion
Legacy EVALUATE in LAMBDA: Build/Test LAMBDAs from Sheet
Dunno, I suppose it's to do with exception handling - some other languages also need a terminator of some sort. The TYPE function was used instead of ISERROR because it always returns a single value so can handle array parameters more easily.
I'd be interested to know if there's a workaround for the recursion limits which are quite restrictive at the moment. If Excel doesn't optimise tail recursion something like this might work (though I struggle to get my head around it!)
lori_m PeterBartholomew1 This got me going down a rabbit hole, and I certainly don't imply that I know what I've been doing, but I think it's helping me get my head wrapped around it (slowly).
Based on the links I ended up doing some googling, and this is something I missed skimming the Microsoft https://www.microsoft.com/en-us/research/blog/lambda-the-ultimatae-excel-worksheet-function/ the first time: the GIF shows their construction of the Z/fixed point combinator.
I searched a bit more to find a derivation of the Z combinator, and came across https://thenewobjective.com/types-and-programming-languages/deriving-the-z-combinator#fixed-points-and-combinators, which seemed reasonably "accessible" (obvious scare quotes due to subject material). So I set about trying to step through these constructions in my LET/LAMBDA testing spreadsheet; please see attached. There were a few interim steps that I couldn't figure out how to implement, but ultimately the final "fact_16" is very similar to the "my_fact" I got from the Microsoft gif. I'm going to be getting some textbooks I haven't looked at in 20 years out over the weekend to try and remember the very little I "learned" about lambda calculus to facilitate making sense of this, because its mostly been pattern matching through the exercise.
Good info, thanks for posting. I'd recommend 'Computerphile' which has some nice videos at a basic level (like mine). After going through some of that material I concluded the modified combinator method I linked to before needs a while loop so wouldn't help with recursion limits.
There's also a 'Funcalc' spreadsheet project that is the basis of some of the Microsoft Research material, details of which can be found here. It does look like Excel is heading toward a fully fledged functional programming language!