Tree farm [string:1: attempt to call nil]

So straight forward:

• I got a tree farm program.
• It's buggy.
• Here's the code:
  Spoiler

  Also on pastebin: zcmDcV15

  --(( Variables ))--
  
  local cutCount = 0
  
  local moves = {
    dig = {
  	["f"] = turtle.dig,
  	["u"] = turtle.digUp,
  	["d"] = turtle.digDown,
    },
    move = {
  	["f"] = turtle.forward,
  	["u"] = turtle.up,
  	["d"] = turtle.down,
    },
    attack = {
  	["f"] = turtle.attack,
  	["u"] = turtle.attackUp,
  	["d"] = turtle.attackDown,
    },
  }
  
  --(( Functions ))--
  
  function go(direction, fromNum, toNum)
    while not moves.move[direction]() do
  	if fromNum and toNum then
  	  select(fromNum,toNum)
  	end
  	if not moves.dig[direction]() then
  	  moves.attack[direction]()
  	end
  	sleep(.5)
    end
  end
  
  function select(fromNum, toNum, option)
    if not toNum or fromNum == toNum then
  	turtle.select(fromNum)
  	return true
    end
    for slot = fromNum, toNum do
  	option = loadstring("turtle.getItem"..option.."(slot)")
  	if option() > 0 then
  	  turtle.select(slot)
  	  return true
  	end
    end
    return false
  end
  
  function cutTree()
    if turtle.getItemSpace(1) > 0 then
  	turtle.select(1)
    else
     if not select(5,16,"Space") then
  	 turtle.select(1)
  	 return false
     end
    end
    go("f")
    turtle.select(1)
    while turtle.compareUp() do
  	if not select(5,16,"Space") then
  	  turtle.select(1)
  	  return false
  	end
  	go("u",5,16)
    end
    while not turtle.detectDown() do
  	go("d",5,16)
    end
    if not turtle.back() then
  	for turns = 1, 2 do
  	  turtle.turnLeft()
  	end
  	go("f",5,16)
  	for turns = 1, 2 do
  	  turtle.turnRight()
  	end
    end
    return true
  end
  
  --(( Main program ))--
  
  if not fs.exists("."..shell.getRunningProgram().."Data") then
    file = fs.open("."..shell.getRunningProgram().."Data","w")
    file.write(cutCount)
    file.close()
  else
    file = fs.open("."..shell.getRunningProgram().."Data","r")
    cutCount = tonumber(file.readLine())
    file.close()
  end
  
  term.setCursorPos(1,1)
  term.clear()
  
  while true do
    if turtle.getItemCount(1) < 1 then
  	break
    end
    term.setCursorPos(1,1)
    term.clear()
    print("Remove the log to stop!")
    print()
    print("Have log in slot 1!")
    print("Have saplings in slot 2-4!")
    print()
    print("Trees cut: "..cutCount)
    print()
  
    if not turtle.detect() then
  	if not select(2,4,"count") then
  	  print("Out of saplings!")
  	  break
  	end
  	while not turtle.place() do
  	  moves.attack["f"]()
  	  sleep(.5)
  	end
    end
  
    turtle.select(1)
    if turtle.compare() then
  	if chopTree() then
  	  cutCount = cutCount + 1
  	  file = fs.open("."..shell.getRunningProgram().."Data","w")
  	  file.write(cutCount)
  	  file.close()
  	else
  	  print("Failed to chop tree!")
  	  break
  	end
    end
  
    sleep(.5)
  end
  
  turtle.select(1)

So the error that I'm getting is:

string:1: attempt to call nil

I've never seen this error before and I can't find any solutions on the interwebz.

EDIT:​ I caught one typo:

-- on line 118
    if not select(2,4,"count") then
-- misspelled count
-- first letter should be uppercase
    if not select(2,4,"Count") then

Now I'm getting another error, and I haven't seen this one either before:

string:1: Expected number

This kind of error usually indicates that you have tried to use loadstring on a bit of code that was syntactically valid (so loadstring turned it into a function named "string") but then you ran it and it was missing something.

option = loadstring("turtle.getItem"..option.."(slot)")

Works if you feed it "Space" or "Count" as the option. But at one point you fed it "count"

if not select(2,4,"count") then 

You might have fed it something bad in other places, I'm not sure. But this is kinda a wonky use of loadstring, methinks. You should just say "turtle["getItem"..option](slot)" instead of using loadstring to retype option and then running option here. And not just because loadstring errors are difficult to debug (really you should always pcall functions made by loadstring, I should do that myself). Calls of loadstring require the creation of a whole new virtual environment, they're super inefficient ways to do things that you might do any other way.

ChunLing, on 31 October 2012 - 07:44 AM said:

This kind of error usually indicates that you have tried to use loadstring on a bit of code that was syntactically valid (so loadstring turned it into a function named "string") but then you ran it and it was missing something.

option = loadstring("turtle.getItem"..option.."(slot)")

Works if you feed it "Space" or "Count" as the option. But at one point you fed it "count"

if not select(2,4,"count") then 

You might have fed it something bad in other places, I'm not sure. But this is kinda a wonky use of loadstring, methinks. You should just say "turtle["getItem"..option](slot)" instead of using loadstring to retype option and then running option here. And not just because loadstring errors are difficult to debug (really you should always pcall functions made by loadstring, I should do that myself). Calls of loadstring require the creation of a whole new virtual environment, they're super inefficient ways to do things that you might do any other way.

Ah good idea with the

turtle["getItem"..option](slot)

idea! Thanks!
I'm going to try it now..

You still have to feed it correctly, only "Space" and "Count", but at least if it fails you know instantly what failed. And it's much faster execution-wise.

But what if I do

option = option:lower()
option = option:gsub("%a",string.upper(),1)

Wouldn't that work?

… :P/>/>
Just feed it correctly. I mean, yeah, you can use string functions to ensure that user entered strings are more rather than less correct, but for the fixed strings in your code, they should just be right.

You had me going there. :P/>/>

Thanks for the help btw!