bios:339: [string "def"]:52: 'then' expected

Hi i keep getting this error bios:339: [string "def"]:52: 'then' expected when i try to run my code
its saying im missing a then on line 52 but it has one

any help is greatly appreciated

Mon = peripheral.wrap("top")
local function centerText(text)
  x,y = m.getSize()
  x1,y1 = m.getCursorPos()
  Mon.setCursorPos((math.floor(x/2) - (math.floor(#text/2))), y1)
  Mon.write(text)
end
local function defence()
	centerText("===============================================")
	Mon.setCursorPos(1, 2)
	centerText("WARNING!")
	Mon.setCursorPos(1, 3)
	centerText("INCOMING MISSILE")
	Mon.setCursorPos(1, 4)
	centerText("ACTIVATING FORCEFIELD")
	Mon.setCursorPos(1, 5)
	redstone.setOutput("right", true)
	minutes = 5
	seconds = 0
	clocktime = minutes+seconds
repeat
	if seconds == 0 then
	minutes = minutes-1
	seconds = 60
end
if minutes == -1 then
	break
end
	seconds = seconds-1
if seconds < 10 then
	zero = 0
else
	zero = ""
end
	Mon.setCursorPos(1, 5)
	centerText("Forcefield will be active for: "..minutes..":"..zero..seconds)
	Mon.setCursorPos(1, 6)
	centerText("===============================================")
until minutes == -1
	sleep(0.1)
	Mon.setCursorPos(1, 5)
	Mon.clearLine()
	CenterText("FORCEFIELD DEACTIVATED!")
	sleep(0.5)
	redstone.setOutput("right", false)
end
function check()
	if redstone.getInput("left") == true then --THIS IS THE LINE THAT I GET AN ERROR WITH
		defence()
	end
	elseif redstone.getInput("left") == false then
		check()
	end

The line you've flagged looks valid to me, but a few lines under it I can see you're trying to pull an "elseif" on an "if" block you've already "end"ed.

Just for kicks, try this:

if redstone.getInput("left") then defence() else check() end

Edit:

Well, that'd run directly into another issue - spam of recursive function calls causing a stack overflow and hence script crash - so maybe try this:

local function check()
	while true do                                            -- Start an indefinitely repeating loop.
		if redstone.getInput("left") then defence() end  -- Perform the check.
		os.pullEvent("redstone")                         -- Wait for a redstone state change.
	end
end

ok will give it a try as soon as im home thanks

ok i have tried it but it still gives the exact same error

heres the code

Mon = peripheral.wrap("top")
local function centerText(text)
  x,y = m.getSize()
  x1,y1 = m.getCursorPos()
  Mon.setCursorPos((math.floor(x/2) - (math.floor(#text/2))), y1)
  Mon.write(text) 
end
local function defence()
    centerText("===============================================")
    Mon.setCursorPos(1, 2)
    centerText("WARNING!")
    Mon.setCursorPos(1, 3)
    centerText("INCOMING MISSILE")
    Mon.setCursorPos(1, 4)
    centerText("ACTIVATING FORCEFIELD")
    Mon.setCursorPos(1, 5)
    redstone.setOutput("right", true) --Change "right" to the side thats will activate the forcefield
    minutes = 5
    seconds = 0
    clocktime = minutes+seconds
repeat
    if seconds == 0 then
    minutes = minutes-1
    seconds = 60
end
if minutes == -1 then
    break
end
    seconds = seconds-1
if seconds < 10 then
    zero = 0
else
    zero = ""
end
    Mon.setCursorPos(1, 5)
    centerText("Forcefield will be active for: "..minutes..":"..zero..seconds)
    Mon.setCursorPos(1, 6)
    centerText("===============================================")
until minutes == -1
    sleep(0.1)
    Mon.setCursorPos(1, 5)
    Mon.clearLine()
    CenterText("FORCEFIELD DEACTIVATED!")
    sleep(0.5)
    redstone.setOutput("right", false) --Change "right" to the side thats will activate the forcefield
end
local function check()
	    while true do-- Start an indefinitely repeating loop.
			    if redstone.getInput("left") then defence() end  -- Perform the check.
			    os.pullEvent("redstone") -- Wait for a redstone state change.
	    end
end

Angel_Code, on 19 March 2014 - 10:07 AM said:

ok i have tried it but it still gives the exact same error
-code snip-

are you sure? doesn't error for me.

Thanks guys i got it working

I don't know if anyone already caught this, and it doesn't matter since fixing the original code doesn't really fix it as you then have to deal with a stack overflow, but the reason the original code didn't work right was because of where you placed your end's:

function check()
	    if redstone.getInput("left") == true then
			    defence()
	    end--this shouldn't be here, an if statement only needs one end, which should come after any elseif or else statements, this was what was causing your weird compiler error
	    elseif redstone.getInput("left") == false then
			    check()
	    end--this should be the only end for the entire if statement
--but here is another issue, there is no end for the "check" function, you would get a compiler error here as well

it should read:

function check()
	    if redstone.getInput("left") == true then
			    defence()
	    elseif redstone.getInput("left") == false then
			    check()--this causes a stack overflow eventually, the code will compile and run, but it will crash at runtime
	    end
end

Bomb Bloke's initial reply did mention the issue with the end before the elseif.