Mining Turtle programm that doesn‘t work

function D()
 if
 turtle.detect()
 then

       turtle.dig()
 end
 end

function PD()
 if not
 turtle.detectDown()
 then
       turtle.select(2)
       turtle.placeDown()
 end
 end


for a=1,3 do
  turtle.dig()
  turtle.forward()
  PD()
  D()
  turtle.digUp()
end

  turtle.turnRight()

for b=1,4 do
  turtle.dig()
  turtle.forward()
  PD()
  D()
  turtle.digUp()
end

  turtle.turnLeft()
  turtle.turnLeft()

for c=1,4 do
  turtle.forward()
  PD()
  D()
end

for d=1,4 do
  turtle.dig()
  turtle.forward()
  PD()
  D()
  turtle.digUp()
end
  turtle.turnRight()
  turtle.turnRight()
end

for e=1,4 do
  turtle.forward()
  PD()
  D()
end

  turtle.turnLeft()

 end

  turtle.turnLeft()
  turtle.turnLeft()
 end
 for f=1,4 do
  turtle.forward()
 end

 turtle.drop()

 end