ComputerCraft Caliper/Fill

local distance = 0
local length, width

--[[Movement/Dig Functions]]--

function checkBelow() -- Replace block below with slot 1
    turtle.select(1)
    if turtle.compareDown() == false then
        turtle.digDown()
        turtle.place()
    end
end

function digFor() -- Dig forward
    while turtle.detect() do
        turtle.dig()
    end
end

function back(n)
    for i=1,n do
        turtle.back()
    end
end

--[[Caliper Functions]]--

function caliper()
    while turtle.detect() == false do
        turtle.forward()
        distance = distance + 1
    end
    back(distance)
    print("Distance is: ")
    print(distance)
    distance = 0
end

--[[Fill Functions]]--

function fill()
    lengthOne()
    checkBelow()
    turtle.turnLeft()
    spiralIn()
end

function lengthOne()
    for i=1,length-1 do
        checkBelow()
        digFor()
        turtle.forward()
    end
end

function spiralIn()
    while length - 1 > 0 do
        for i=1,2 do -- Dig sides of same length twice
            for j=1,length-1 do -- Dig forward and check
                digFor()
                turtle.forward()
                checkBelow()
            end
            turtle.turnLeft() -- Turn upon completion of row
        end
        length = length - 1 -- Decrease side length every two rows
    end
end

--[[Main]]--

print("Caliper or Fill? (c or f)")
local choice = read()

if choice == "c" then
    caliper()
end
if choice == "f" then
    print("How far forward? (length)")
    length = tonumber(read())
    print("How far left? (width)")
    width = tonumber(read())
    fill()
end