Computercraft Recursive Tree Harvesting

-- Example of recursion to dig branched or large trees
-- ensure there is a log of the tree  type in slot 1

function isTree(direction)
    result = false

    turtle.select(1) --select slot 1 which contains wood
    if direction == "up" then -- check block above
        if turtle.compareUp() then -- wood block above
            result = true
        end
    elseif direction == "down" then -- check block down
        if turtle.compareDown() then -- wood block below
            result = true
        end
    elseif direction == "forward" then -- check block ahead
        if turtle.compare() then -- wood block ahead
            result = true
        end
    end

    return result -- true/false
end

function mineTree(direction)
    --RECURSIVE FUNCTION - BEWARE!

    -- check if block in front is valuable. If so dig it
    -- direction only set to up/down if already called recursively
    if direction == "up" then
        if isTree("up") then
            turtle.digUp()
        end
        -- move up into space dug out
        turtle.up()
        -- check if item in front is valuable
        if isTree("forward") then
            mineTree("forward")
        end
        --check right side
        turtle.turnRight()
        if isTree("forward") then
            mineTree("forward")
        end
        --check behind
        turtle.turnRight()
        if isTree("forward") then
            mineTree("forward")
        end
        --check left side
        turtle.turnRight()
        if isTree("forward") then
            mineTree("forward")
        end
        --return to front
        turtle.turnRight()
        -- end of recursion so return to previous position
        turtle.down()
    end
    if direction == "down" then
        if isTree("down") then
            turtle.digDown()
        end
        -- move down into space dug out
        turtle.down()
        -- check if item in front is valuable
        if isTree("forward") then
            mineTree("forward")
        end
        --check right side
        turtle.turnRight()
        if isTree("forward") then
            mineTree("forward")
        end
        --check behind
        turtle.turnRight()
        if isTree("forward") then
            mineTree("forward")
        end
        --check left side
        turtle.turnRight()
        if isTree("forward") then
            mineTree("forward")
        end
        --return to front
        turtle.turnRight()
        -- end of recursion so return to previous position
        turtle.up()
    end
    if direction == "forward" then
        if isTree("forward") then
            turtle.dig()
            turtle.forward()
            if isTree("up") then
                mineTree("up")
            end
            if isTree("down") then
                mineTree("down")
            end
            -- check if item in front is valuable
            if isTree("forward") then
                mineTree("forward")
            end
            --check left side
            turtle.turnLeft()
            if isTree("forward") then
                mineTree("forward")
            end
            -- check right side
            turtle.turnRight()
            turtle.turnRight()
            if isTree("forward") then
                mineTree("forward")
            end
            turtle.turnLeft()
            -- end of recursion so return to previous position
            turtle.back()
        end
    end
end