content: module HsLexerPos where
  
  data Pos = Pos { char, line, column :: !Int } deriving (Show)
  
  simpPos (Pos _ l c) = (l,c)
  
  -- Some functions still put fake char positions in Pos values, so...
  instance Eq Pos where p1 == p2 = simpPos p1 == simpPos p2
  instance Ord Pos where compare p1 p2 = compare (simpPos p1) (simpPos p2)
  
  
  startPos = Pos { char=0,
  		 line=1,
  		 column=1  -- The first column is designated column 1, not 0.
  	       }
  
  nextPos :: Pos -> String -> Pos
  nextPos = foldl nextPos1
  
  nextPos1 :: Pos -> Char -> Pos
  nextPos1 (Pos n y x) c =
      case c of
        -- The characters newline, return, linefeed, and formfeed, all start
        -- a new line.
        '\n'  -> Pos (n+1) (y+1) 1
        '\CR' -> Pos (n+1) (y+1) 1
        '\LF' -> Pos (n+1) (y+1) 1
        '\FF' -> Pos (n+1) (y+1) 1
        -- Tab stops are 8 characters apart.
        -- A tab character causes the insertion of enough spaces to align the
        -- current position with the next tab stop.
        -- + (not in the report) the first tab stop is column 1.
        '\t'  -> Pos (n+1) y (x+8-(x-1) `mod` 8)
        _ -> Pos (n+1) y (x+1)
  