Mining Program help?

a = 0
for i = 1,383 do
turtle.dig()
turtle.forward()
turtle.digUp()
if a == 6 then
if turtle.detectDown() then
turtle.back()
turtle.select(1)
turtle.place()
end
a = 0
turtle.forward()
else
a = a + 1
end
end

This returns
bios :206: [string "tunnel"]:11: '=' expected

Be sure to format your code, better for us reading it to help you, as well as helps you spot mistakes as well.

Saying that, I do not spot any mistakes in the code you posted. Is this the entire code of the program?
Is this also part of the file called tunnel?