Recursive LAMBDA implementation of Excel's REDUCE function.

HIJKPieterse 

Re: your question what is CLAMBDA?

recursive LAMBDA PARAMETERS  are : [initial_value,  array,    CLAMBDA ]
recursive LAMBDA ARGUMENTS   are:  (0,                  {1,2,3},   LAMBDA(acc,cv, acc+cv) ]

Mapping PARAMETERS to ARGUMENTS, we get:
initial_value => 0
array           => {1,2,3}
CLAMBDA  => LAMBDA(acc,cv, acc+cv)

CLAMBDA is a LAMBDA function that tells REDUCE how to combine the previous accumulator with the current_value, to produce the new accumulator. In my example I am just summing [accumulator + current_value] which results in the sum of the inputted array.

Re: Recursion LIMITS

You are correct -- the maximum vector size I was able to use in the recursive function was about 2,700
while in the real Excel REDUCE I could easily use a vector size of 1 million
=REDUCE(0, SEQUENCE(1,1000000,1,1), LAMBDA(acc,cv, acc+cv))

Lastly:

this code demonstrates how one COULD write Excel's REDUCE in as a Recursive Excel LAMBDA function. It in no way implies one should write it this way.  However, if you need to do looping where the number of repetitions is unknown, you will likely need to use recursion.

Hope your questions were answered.