Global Variable Help?

I'm writing an API for digging with turtles that allows a program using it to keep track of where it is. However, I'm having trouble getting the global variables to work the way I want.

-- This is an API used in programs

dist_x = 0
dist_y = 0
dist_z = 0
dist_r = 0

function update(n)

if n=="fwd" then

  if dist_r == 0 then
   dist_z = dist_z + 1

  elseif dist_r == 90 then
   dist_x = dist_x + 1

  elseif dist_r == 180 then
   dist_z = dist_z - 1

  elseif dist_r == 270 then
   dist_x = dist_x - 1

  end

elseif n=="right" then
  dist_r = dist_r + 90

elseif n=="left" then
  dist_r = dist_r - 90

elseif n=="up" then
  dist_y = dist_y + 1

elseif n=="down" then
  dist_y = dist_y - 1

end

while dist_r >= 360 do
  dist_r = dist_r - 360
end
while dist_r < 0 do
  dist_r = dist_r + 360
end

--bug testing
print(dist_x)
print(dist_y)
print(dist_z)
print(dist_r)

end


function fwd(n)
local x
for x=1, n or 1 do
  while not turtle.forward() do
   turtle.dig()
   turtle.attack()
  end
  update("fwd")
end
end


function up(n)
local x
for x=1, n or 1 do
  while not turtle.up() do
   turtle.digUp()
   turtle.attackUp()
  end
  update("up")
end
if (n or 1) < 0 then
  down(-n)
end
end

function down(n)
local x
for x=1, n or 1 do
  while not turtle.down() do
   turtle.digDown()
   turtle.attackDown()
  end
  update("down")
end
if (n or 1) < 0 then
  up(-n)
end
end

function left(n)
local x
for x=1, n or 1 do
  turtle.turnLeft()
  update("left")
end
for x=n or 1, -1 do
  turtle.turnRight()
  update("right")
end
end

function right(n)
local x
for x=1, n or 1 do
  turtle.turnRight()
  update("right")
end
for x=n or 1, -1 do
  turtle.turnLeft()
  update("left")
end
end

function dig()
while not turtle.dig() do end
end

The idea is to run the functions like so:

dig.up(2)
dig.right()
dig.fwd(6)

The "dig.dist_y" variable should be "2" because it went up two blocks, "dig.dist_x" should be "6", "dig.dist_r" should be "90", and "dig.dist_z" should still be "0". However, when I actually run the API, those variables always return "0". I presume this is because when the functions edit the variables, it just creates local variables that are cleared when the function terminates. How do I make sure I'm assigning the new values to the global variables?

Flexico, on 08 December 2015 - 04:16 AM said:

However, when I actually run the API, those variables always return "0".

Every time you "run" the API (or os.loadAPI() it), that'll reset your variables, as the first few lines set 'em to 0. But outside of that, it appears to work as you expect it to…?

Perhaps you could give some more context as to how you're using this API.

A couple of things that do stand out at me:

function dig()
while not turtle.dig() do end
end

This function will always attempt to dig once, but if the dig attempt fails (eg because there was nothing to dig, or bedrock), odds are it'll get stuck in an infinite loop of trying to do the impossible. You may've meant:

function dig()
repeat until not turtle.dig()
end

Also, when initiating a "for" loop, eg:

for x=1, n or 1 do

… the counter variable (in the above case "x") is automatically created as local to that loop. Defining a local "x" before the loop is a redundant step: that one won't actually get used inside it, as the loop's own local "x" takes precedence over the upvalue.

Ok, I ended up fixing it with a function that returns the values instead of referencing the variables directly, and that seems to work! Also fixed dig(); there just wasn't supposed to be a "not" in there. XD