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module Language.Haskell.Lexer.Position where
-- | The posisiotn within a file.
data Pos = Pos { char, line, column :: !Int } deriving (Show)
-- | The line and column numbers of a position.
simpPos :: Pos -> (Int,Int)
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)
-- | The first column is designated column 1, not 0.
startPos :: Pos
startPos = Pos { char = 0, line = 1, column = 1 }
-- | Advance position by a string.
nextPos :: Pos -> String -> Pos
nextPos = foldl nextPos1
-- | Advance position by a single character.
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.
'\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)
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