function or while loop not working?

code:
function sf()
while not turtle.forward() do
turtle.dig
end
end

then i try to start the program i get:
bios:338: [string "testfunc"]:4: '='
expected

i need this code for a program that digs a room with without grawel getting in the way.

turtle.dig needs to be turtle.dig()

EDIT: besides that, I think the problem is somewhere else in the code if it still gives an error, therefore, post the entire code if it does :P/>

i'm blind. thank you.