Tail-recursion was Re: [TUHS] Lorinda Cherry - COFF

23 Feb 2022

My all time favorite presentation on tail-recursion:

https://www.youtube.com/watch?v=-PX0BV9hGZY

On 2/22/22 4:39 AM, Ralph Corderoy wrote:
...
  Hi Otto,

  MacOS uses the GNU implementation which has a
long standing issue with
 deep recursion.  It even cannot handle the tail recursive calls used
 here and will run out of its stack.  When learning dc and seeing it relied on tail
calls, the first thing
 I did was check it did tail-call elimination, and it did.  That was
 GNU dc.

 Trying just now, I see no growth in memory usage despite heavy CPU load
 shown by TIME increasing.

      $ dc
      !ps u `pidof dc`
      USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
      ralph    11489  0.0  0.0   2332  1484 pts/1    S+   10:33   0:00 dc
      [lmx]smlmx
      ^C
      Interrupt!
      !ps u `pidof dc`
      USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
      ralph    11489 75.5  0.0   2332  1488 pts/1    S+   10:33   0:46 dc

 The memory used remained at that level during the macro execution too,
 watched from outside.

 Do you have more detail on what GNU dc can't handle?  dc without
 tail-call elimination is a bit crippled.