Non-Recursive Vein Miner

local sides={[0]="north",[1]="east",[2]="south",[3]="west",[4]="up",[5]="down"}
local move_vect={[0]=vector.new(0,0,-1),[1]=vector.new(1,0,0),[2]=vector.new(0,0,1),[3]=vector.new(-1,0,0),[4]=vector.new(0,1,0),[5]=vector.new(0,-1,0)}
local facing=0
local mining={vector.new(0,0,0)}
local junkslots={1,2,3,4}

local function left()
    if turtle.turnLeft() then
        facing=(facing-1)%4
        return true
    else
        return false
    end
end

local function right()
    if turtle.turnRight() then
        facing=(facing+1)%4
        return true
    else
        return false
    end
end

local function turnTo(side)
    local diff=(side-facing)%4
    local turn=right
    if diff>2 then
        turn=left
        diff=4-diff
    end
    for i=1,diff do
        turn()
    end
end

local function compareBlock(side)
    local compare=turtle.compare
    local detect=turtle.detect
    if side<4 then
        turnTo(side)
    elseif side==4 then
        compare=turtle.compareUp
        detect=turtle.detectUp
    else
        compare=turtle.compareDown
        detect=turtle.detectDown
    end
    if detect then
        for i,j in pairs(junkslots) do
            turn.select(j)
            if compare() then return false end
        end
        return true
    else
        return false
    end
end

local function scanSides()
    for i,j in pairs(sides) do
        if compareBlock(i) then return i end
    end
    return "no ore"
end

local function whichWay(here,there)
    local move=there:sub(here)
    for i,j in ipairs(move_vect)
        if move==j then return i end
    end
end

local function go(direction)
    if go<4 then
        turnTo(go)
        turtle.dig()
        return turtle.forward()
    elseif go==4 then
        turtle.digUp()
        return turtle.up()
    else
        turtle.digDown()
        return turtle.down()
    end
end

local function notRecursive
repeat
    local mine=scanSides()
    if move_vect[mine] == nil then --#if no ore found
        if #mining>1 then --#if not at start
            if go(whichWay(mining[#mining],mining[#mining-1]) then --#try to go back 1
                table.remove(mining) --#remove where we came from if successful
            else
                --#something has gone wrong
            end
        end
    else    --#if ore found
        if go(mine) then    --#dig it and move there
            table.insert(mining,mining[#mining]:add(move_vect[mine])) --#update position
        else
            --#something has gone wrong, possibly gravel, haven't put and handling in for that
        end
    end
until #mining==1
end