CAAB Basalt coin gen

function voidInv()
    turtle.select(1)
    for i=1,16 do
        turtle.select(i)
        turtle.drop()
    end
end

function isBasalt()
    local blockID
    local success, data = turtle.inspectDown()
    if success then
       blockID = data.name
    end

    if data.name == "minecraft:basalt" then
        return true
    else
        return false
    end
end

function mine()
    turtle.select(1)
    while not isBasalt() do
        turtle.select(1)
    end
    turtle.digDown()
end

function craft()
    local inv = {11, 12, 15, 16}
    for i=1,2 do
        turtle.transferTo(inv[1], 1)
        turtle.transferTo(inv[2], 1)
        turtle.transferTo(inv[3], 1)
        turtle.transferTo(inv[4], 1)
        turtle.craft()
    end

end

function uppies()
    turtle.select(1)
    turtle.dropUp()
end

local function main()
    while redstone.getInput("back") do
        for i = 1, 4 do
            mine()
        end
        craft()
        uppies()
    end
    os.pullEvent("redstone")
    voidInv()
end

voidInv()
while true do
    main()
end