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Pulling along set of directions

Posted by Thalir on Wed 15 Aug 2007 12:36 AM — 8 posts, 29,991 views.

Thalir #0
For example, I have a set of different directions running from my home to city A, b, C:
n, e, s, w, u, d <--- in this format

If I pull a cart north, there are two messages:
i) You pull a cart north <---- When I start
ii) You have pulled a cart north <---- Once I've done pulling and am in the next room.

How might I tackle this, to trigger cart pulling along the set of directions I provide, plus recognize I've moved into a new room and use the next available direction?

Would it be possible to store these dirs in a text file and read from them?

I'm guessing the solution is to somehow use the key order by putting the dirs in a lua table.
=================================
In summary:
-How to pull a cart, following the directions?
-How to switch the set of directions (cities)?
-And a way to stop and start, but still know which dir I'm up to?
================================
I'd also like to express my utmost gratitude for all those helpful people replying to my previous posts, I am very glad mushclient has such great technical support.


Shaun Biggs USA #1
I would just create a table with the directions listed in order. cartdirs={"n", "e", "s", "w", "u", "d"} Then have a regex trigger match="^You pull a cart (north|south|east|west|up|down)$"

Then just have a function like this:

function nextpull()
  if #cartdirs > 0 then
    Send( "pull cart "..cartdirs[1] )
    table.remove( cartdirs, 1 )
  end
end


To make it start or resume, just have an alias to enable the trigger and send the first direction. To pause it, just disable the trigger.
Thalir #2
Thanks, I'd like to ask, what does
#cartdirs > 0
mean? Is that a check to see if the table is empty
Shaun Biggs USA #3
You are correct. #varname tells you how many elements are in the table. if #cartdirs == 0, then the table is empty.
David Haley USA #4
As a minor note, the #table syntax only works for arrays i.e. tables with only numeric keys. And strictly speaking, the # operator also only returns the highest integer key in the contiguous range starting from 1. (At least, for sparse arrays.)

E.g.

[david@thebalrog:~]$ cat test.lua
t = {}
t.a = 1
t.b = 1
print(#t)
t = {}
t[1] = 1
t[2] = 1
print(#t)
t[10] = 1
print(#t)
[david@thebalrog:~]$ lua test.lua
0
2
2


This can be tricky, because e.g.

[david@thebalrog:~]$ cat test.lua
t = {}
t[10] = 1
print(#t)
[david@thebalrog:~]$ lua test.lua
0


The proper way to check if a table is empty, "proper" meaning one that will always work, is to see if next returns nil for that table. If next(t) == nil, then the table is empty; if next(t) ~= nil, the table has something in it.
Shaun Biggs USA #5
True, but in this case, the array has to be sequential and starting with an index of 1 for the function to work, so #t will do the job better than next(t) will. It is important to make the distinction between the two though, so thanks for clarifying.
David Haley USA #6
Main reason I pointed it out was that I've been bitten in the neck a few times by this. It's interesting to follow Lua list traffic a bit because this is something of a point of contention.

For instance, if you set indices 1, 2 and 4, you get #t == 4, but if you set 1, 2 and 10, you get #t == 2... some people think the # operator isn't quite right because it doesn't always do what you think it should do, but then sometimes it does something you thought it wasn't supposed to do, and all that stuff.
Shaun Biggs USA #7
You can also use table.setn(t, 20) to set the size of the table to 20 elements. At that point, you can have 2 elements filled, and #t would return 20. And even then table.remove(t) will remove the item in #t (even if there was nothing there to begin with), so #t will then return 19. Point being... be careful with data set construction and proper removal of elements.