🚀 go-pugleaf

On Tue, 5 Jun 2018 15:42:33 +0100, Gareth's Downstairs Computer
<headstone255.but.n...@yahoo.com> wrote:
>On 05/06/2018 15:28, Andrew Swallow wrote:
>> On 04/06/2018 17:16, Gareth's Downstairs Computer wrote:
>>> Recursion : see  recursion.
>>>
>>> As a recursive "elegant" solution,
>>>
>>> factorial (1,000,000) is likely to
>>> crash most systems
>> 
>> Factorial is a simple loop.
>> 
>
>The discussion was not about iteration but the
>claimed elegance of recursion.
>
>However, another iterative process where recursion is
>unnecessary is the walking of trees; certainly a B Tree
>where all are sorted, for you take the standard approach
>of walking a maze (a maze with no internal doors!!!!!) of
>always taking the leftmost branch, by always first going
>for the lowest branch

Below a simple version of the "standard" DEC routine for number output -- using
the stack to reverse the order of digits.  Recursion is also very useful for
generating permutations and combinations.


[best viewed with fixed-width typeface]


;Recursive decimal output routine -- number in T1
;
; Since a PDP10 address fits in the right half of a word, the left half
; can be used to hold each digit.  On other machines, it would be PUSHed
; onto the stack and subsequently POPed off.

DECOUT: IDIVI T1, 10.                   ;remainder in T2
        HRLM  T2, (P)                   ;save stack space -- use left half
        SKIPE T1                        ;anything left?
         PUSHJ P, DECOUT                ;yes, call DECOUT recursively
        HLRZ  T2, (P)                   ;retrieve stashed digit
        ADDI  T2, "0"                   ;convert to ASCII
        OUTCHR  T2                      ;
        POPJ  P,                        ;