This was intended for https://forum.nim-lang.org/t/2816 - but Araq beat me to it...  :rofl: 

I get similar results: the perl program is about three times faster.  :(

OK, let's ``use Time::HiRes`` ``import times`` `(etc) <https://gist.github.com/lbmn/d424dd0c8c85fa195743356fc133235a>`_ for some ad-hoc time-subtracting.

About 24.5% of the Nim program's execution time is spent on ``surface.write_to_png image``, which is actually a bit faster than Perl, so the cairo bindings are not the problem.

About 75% of the Nim program's execution time is spent on ``draw(level, t1)``.  That proc uses recurses multiple times (level 12 to 3), but it uses about 69% of the total program time when level is 4, in which case the loop is executed 6561 times.  So let's zoom in on this loop...

**Wowzers, 88% of the time in that inner loop is spent just on concatenating seqs! So that is our problem...**

I don't know what the best solution is, but one `step in the right direction <https://gist.github.com/lbmn/32f20a60e8cc4b5157c9a94fa3adcafc>`_ would be to allocate next before the for loop in draw():

```nim

var next: trias = newSeq[trian]()```

And to use add inside the loop:

```nim

next.add @[
  (HEAD, left, right),
  (left, LEFT, tail),
  (right, tail, RIGHT)
]
```

And now we're 18% faster than perl.  :)