Re: Advent of Code, Day 19

[Gautier Write-Only Address <gautier_niouzes@hotmail.com>]

For me the first part was the tough one. I've tried for too long to structure the rules verification like this
procedure Verify_Rule (...) is
  ...
  procedure Verify_Rule_List (...) is
  ...
  begin
    loop on the list, call recursively Verify_Rule
  end;
end;
But a loop cannot be used here, each subrule can consume a variable range of characters in the string and there are multiple tails of the string for the next subrule for the loop.
So the solution in that case was to delegate everything further to recursion.

Part two was (in my case) a matter of applying the indicated rules modification.
    if part = 2 then
      rule (8)  := (is_terminal => False, max => 3, alt => 2, sub => (42, 42,  8, -1, -1));
      rule (11) := (is_terminal => False, max => 5, alt => 3, sub => (42, 31, 42, 11, 31));
    end if;