Computercraft - Turtle Cylinder Digger

args = {...}

radius = 15
height = 10

if tonumber(args[1]) ~= nil and tonumber(args[2]) ~= nil then
    radius = args[1]
    height = args[2]
end

xCoord = 0
zCoord = 0
yCoord = 0

xStartRing = 0
zStartRing = 0

orientation = 4
orientations = {"north", "east", "south", "west"}

zDiff = {-1, 0, 1, 0}
xDiff = {0, 1, 0, -1}


function left()
    orientation = orientation - 1
    orientation = (orientation - 1) % 4
    orientation = orientation + 1
    turtle.turnLeft()
end



function right()
    orientation = orientation - 1
    orientation = (orientation + 1) % 4
    orientation = orientation + 1

    turtle.turnRight()
end



function moveForward()
    xCoord = xCoord + xDiff[orientation]
    zCoord = zCoord + zDiff[orientation]

    moved = false
    while not(moved) do
        turtle.dig()
        moved = turtle.forward()
    end
end



function moveUp()
    yCoord = yCoord + 1

    turtle.digUp()

    moved = false
    while not(moved) do
        moved = turtle.up()
    end
end

function moveDown()

    yCoord = yCoord - 1
    turtle.digDown()

    moved = false

    while not(moved) do
        moved = turtle.down()
    end

end

function look(direction)
    while direction ~= orientations[orientation] do
        right()
    end
end


function round(n)
    decimal = n - math.floor(n)
    if decimal >= 0.5 then
        return math.ceil(n)
    else
        return math.floor(n)
    end
end

function withinRadius(x, z)
    return round( math.sqrt((x * x) + (z * z)) ) <= radius
end


function forwardWithinRadius()

    xNext = xCoord + xDiff[orientation]
    zNext = zCoord + zDiff[orientation]

    return withinRadius(xNext, zNext)
end

function gotoEdge()
    while forwardWithinRadius() do
        moveForward()
    end

    left()

    xStartRing = xCoord
    zStartRing = zCoord
end

function digRing()

    repeat

        while forwardWithinRadius() do
            moveForward()
        end
        while not(forwardWithinRadius()) do
            left()
        end
        moveForward()
        right()

    until xCoord == xStartRing and zCoord == zStartRing

    left()
    left()
    for i = 1,radius do
        moveForward()
    end
    left()
    left()
end

function digLayer()
    r = radius
    for i = 1,r do
        radius = i
        gotoEdge()
        digRing()
    end
end

function digCylinder()
    for i = 1,height do
        digLayer()
        moveDown()
    end
end

digCylinder()