haskell - parse error in nested if/do blocks -

defaultfilename :: [char] defaultfilename = "test.log"  defaultsearchname :: string defaultsearchname = "xyz" 

this code can compiled:

a3 :: int -> [[char]] -> io [char] a3 index arg =    if null arg           <- putstrln "no parameters have been passed."       <- putstrln $ "1 default search string: " ++ defaultsearchname       <- putstrln ("2 default file name: " ++ defaultfilename)       return defaultfilename     else return (arg!!index) 

once add if-then-else, cannot compile anymore

a3 :: int -> [[char]] -> io [char] a3 index arg =    if null arg           <- putstrln "no parameters have been passed."       <- putstrln $ "1 default search string: " ++ defaultsearchname       <- putstrln ("2 default file name: " ++ defaultfilename)       if index == 0          return defaultsearchname         else return defaultfilename     else return (arg!!index) 

why???? frustrating every single step.

your code compiles fine. sure don't have tabs , spaces interleaved there indentation?

try ghci -fwarn-tabs yourfile.hs