How to write a program to output multiple results

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(10-26-2020 06:54 PM)Albert Chan Wrote:  

(10-26-2020 01:23 PM)pinkman Wrote:  Yes good approach, but there is no flatten function on the Prime.

We should request it !

I was looking at XCas source misc.cc, I discovered there is an undocumented flatten1

XCas> flatten1([1,2,3,[4,[5]]])       → [1,2,3,4,[5]]

The code also explained why flatten is so fast.
It only scan the list 1 time, adding 1 element at a time, with time complexity of O(n)

We could emulate the functionality of flatten, but time complexity is O(n^2)
Here is a simple implementation. (note that concat is needed, which kills performance.)

Code:

flat(lst) := {
  local h := head(lst);
  return (h == lst) ? h : concat(flat(h), flat(tail(lst)));
}

The discussion is a little difficult for me to understand, so I will continue my study