6 replies to this topic

[Jack]

This error baffles me.

Spoiler

args = {...}
width = tonumber(args[2])
cells = {}
for i = 1,width do
  cells[i] = i
end
function range(index)
  ret = -1
  i = index
  v = cells[i]
  while i <= width and v == cells[i] do
	i = i + 1
	ret = ret + 1
  end
  return ret
end
function selectVertical()
  ret = {}
  dug = {}
  for i = 1,width do ret[i] = 0 end
  for i = 1,width do dug[i] = 0 end
  for i = width,1,-1 do
	ret[i] = 0
	if dug[cells[i]] == 0 then
	  if (i == 1) or (cells[i-1] ~= cells[i]) then
		j = math.random(i, i + range(i))
		ret[j] = 1
		dug[cells[i]] = 1
	  end
	end
  end
  return ret
end

The error (Index expected, got number) is in this line:

ret[j] = 1

I didn't include all the code, only the parts relevant to this problem.

This is part of an implementation of Eller's maze generation algorithm.

[Kingdaro]

My best guess as to what the problem is, is that your range() function overwrites the ret variable you set in your selectVertical() function when you call it. At the line you've pointed out, it's trying to do something like 1[2] = 3, which doesn't really work. Try localizing your variables, so that they're unique to that one function, and it never gets overwritten.

Localization example:

local ret = -1

Though I'm not sure why Lua doesn't have variables automatically localized. Hm.

[grabie2]

As Kingdaro said: Your problem is that you don't have "ret" declared as "local"

@Kingdaro
lua doesn't localize variables automatically, because it has "local" word not "global" and also local variables are more easy to see when they have keyword before them.

[Kingdaro]

grabie2, on 30 December 2012 - 12:36 PM, said:

lua doesn't localize variables automatically, because it has "local" word not "global"

That's like saying "lua has a local keyword because it has a local keyword" though.

grabie2, on 30 December 2012 - 12:36 PM, said:

and also local variables are more easy to see when they have keyword before them.

There's one side of the spectrum, but instead, why not just have each variable local by default and have a "global" or "export" keyword instead? More times than not you'll probably be typing "local" for all of your variables.

To be fair, for CC's API system, you'd need to type "global" for all of your API functions, so.

[Jack]

Wow. So I can declare a variable within the scope of a function and Lua will automatically upgrade it to global. Does this mean that every variable without "local" before its declaration is global by default?

[Kingdaro]

Jack, on 30 December 2012 - 01:48 PM, said:

Wow. So I can declare a variable within the scope of a function and Lua will automatically upgrade it to global. Does this mean that every variable without "local" before its declaration is global by default?

Yep.

[ChunLing]

The reason for this is that it makes programming a good bit more robust. If you don't specify the scope, then hey the scope is global, because it isn't specified anywhere specific. If you do specify it, then hey the place the scope starts is marked with a keyword.

Most languages use the global keyword so that you don't accidentally make things global. Which makes sense. But it does mean that tracking down the beginning of scope for a local (without a helpful IDE) can be more difficult, particularly if the same identifier is used for more than one local value.