Add Comments.tmPreferences to disable indentation on comments. Having an indented commented line in Haskell will sometimes screw up the compiler. For example:

foo :: Int -> Int -> String
foo x y
    | x < y = "Less Than"
    --| x == y = "Equal"
    | x > y = "Greater Than"

main = do
    putStrLn (foo 1 2)

This code will fail to compile with an error: "src/Main.hs:4:20: parse error on input `='"

Move the comment to the beginning of the line like so:

foo :: Int -> Int -> String
foo x y
    | x < y = "Less Than"
--  | x == y = "Equal"
    | x > y = "Greater Than"

main = do
    putStrLn (foo 1 2)

And everything compiles just fine.