Computercraft: melon/pumpkin/sugar_cane farmer

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-- Vrill's melon/pumpkin/sugar_cane farmer --
-- v 1.1 (size: 16 + 16)                   --
--                                         --
-- 1. edit startup                         --
-- 2. shell.run("melon")                   --
-- 3. save                                 --
---------------------------------------------

function isnumber(myvar)
 local num

 if type(myvar)=="number" then return true end
 if type(myvar)~="string" then return false end
 num=tonumber(myvar)
 if num~=nil then return true end
 return false
end

function move(n)
 local can_move=true
 local i
 if n<0 then
  n=-n
  for i=1,n do
   can_move=turtle.back()
   while not can_move do
    print("There is a something on my way!")
    sleep(2)
    turtle.attack()
    can_move=turtle.back()
   end
  end
 else
  for i=1,n do
   can_move=turtle.forward()
   while not can_move do
    print("There is a something on my way!")
    sleep(2)
    turtle.attack()
    can_move=turtle.forward()
   end
  end
 end
end

function moveUp(n)
 local can_move=true
 local i
 if n<0 then
  n=-n
  for i=1,n do
   can_move=turtle.down()
   while not can_move do
    print("There is a something on my way!")
    sleep(2)
    turtle.attackDown()
    can_move=turtle.down()
   end
  end
 else
  for i=1,n do
   can_move=turtle.up()
   while not can_move do
    print("There is a something on my way!")
    sleep(2)
    turtle.attackUp()
    can_move=turtle.up()
   end
  end
 end
end

function itemsInInventory()
 local itmsum=0
 local i

 for i=1,16 do
  itmsum=itmsum+turtle.getItemCount(i)
 end
 if itmsum>0 then
  return true
 end
 return false
end

function dropAll()
 local i=1
 local dropcnt=0

 for i=16,1,-1 do
  dropcnt=turtle.getItemCount(i)
  if dropcnt > 0 then
   turtle.select(i)
   turtle.drop(dropcnt)
  end
 end
end

function refuelMe()
 local i=1
 local fuelcnt=0

 for i=16,1,-1 do
  turtle.select(i)
  fuelcnt=turtle.getItemCount(i)
  turtle.refuel(fuelcnt)
 end

 if itemsInInventory() then
  turtle.turnRight()
  turtle.turnRight()
  dropAll()
  turtle.turnLeft()
  turtle.turnLeft()
 end
end

function GUI(posX,posY,flevel)
 local i

 term.clear()
 term.setCursorPos(1+posX, 1+posY)
 term.write("+-melon/pumpkin/sugar_cane farmer-+")
 for i=2,5 do
 term.setCursorPos(1+posX, i+posY)
 term.write("|                                 |")
 end
 term.setCursorPos(1+posX, 6+posY)
 term.write("+---------------------------------+")

 term.setCursorPos(3+posX, 3+posY)
 print("  <Label> ",os.getComputerLabel())
 term.setCursorPos(3+posX, 4+posY)
 print("  <Fuel Level> ",turtle.getFuelLevel())

 if turtle.getFuelLevel() < flevel then
 for i=5,8 do
 term.setCursorPos(1+posX, i+posY)
 term.write("|                                 |")
 end
 term.setCursorPos(1+posX, 9+posY)
 term.write("+---------------------------------+")
 term.setCursorPos(10+posX, 6+posY)
 print("Not enough fuel!")
 term.setCursorPos(6+posX, 7+posY)
 print("Please feed me with fuel.")
 end
end

--------------------------------
--Locals:
local i
local need_work=false
local fuelneed=80
local aisle_width=1
local field_length=16

fuelneed=field_length*2 + 2 + (aisle_width+1)*2 + 10

while true do

need_work=false
if itemsInInventory() then
 refuelMe()
end
GUI(2,2,fuelneed)
if turtle.detect() then need_work=true end
if turtle.getFuelLevel() < fuelneed then need_work=false end

if need_work then
 moveUp(1)
 for i=1,field_length do
  turtle.dig()
  move(1)
  if turtle.detectDown() then
   turtle.digDown()
  end
 end
 turtle.turnRight()
 --
 move(aisle_width)
 --
 turtle.dig()
 move(1)
 turtle.turnRight()
 if turtle.detectDown() then
  turtle.digDown()
 end
 for i=1,field_length do
  turtle.dig()
  move(1)
  if turtle.detectDown() then
   turtle.digDown()
  end
 end
 turtle.turnRight()
 --
 move(aisle_width+1)
 --
 turtle.turnLeft()
 moveUp(-1)
 dropAll()
 turtle.turnLeft()
 turtle.turnLeft()
end


sleep(10)
end
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--shell.run("melon")
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