-- | Define a position datatype for giving locations in error messages.
module Text.XML.HaXml.Posn
(
-- * Position type
Posn()
-- ** Constructors of a new position
, posInNewCxt -- :: String -> Maybe Posn -> Posn
, noPos -- :: Posn
-- ** Strictifier
, forcep
-- ** Modifiers
, addcol, newline, tab, white
-- ** Accessors
, posnFilename, posnLine, posnColumn
) where
import Char
-- | Source positions contain a filename, line, column, and an
-- inclusion point, which is itself another source position,
-- recursively.
data Posn = Pn String !Int !Int (Maybe Posn)
deriving (Eq)
posnFilename :: Posn -> FilePath
posnFilename (Pn f _ _ _) = f
posnLine, posnColumn :: Posn -> Int
posnLine (Pn _ x _ _) = x
posnColumn (Pn _ _ x _) = x
-- | Dummy value for generated data, where a true source position does
-- not exist.
noPos :: Posn
noPos = Pn "no recorded position" 0 0 Nothing
-- | @posInNewCxt name pos@ creates a new source position from an old one.
-- It is used when opening a new file (e.g. a DTD inclusion), to denote
-- the start of the file @name@, but retain the stacked information that
-- it was included from the old @pos@.
posInNewCxt :: String -> Maybe Posn -> Posn
posInNewCxt name pos = Pn name 1 1 pos
instance Show Posn where
showsPrec _ (Pn f l c i) = showString "file " .
showString f .
showString " at line " . shows l .
showString " col " . shows c .
( case i of
Nothing -> id
Just p -> showString "\n used by " .
shows p )
-- | Just used to strictify the internal values of a position, to avoid
-- space leaks.
forcep :: Posn -> Int
forcep (Pn _ n m _) = m `seq` n
-- | Add n character positions to the given position.
addcol :: Int -> Posn -> Posn
addcol n (Pn f r c i) = Pn f r (c+n) i
-- | Add a newline or tab to the given position.
newline, tab :: Posn -> Posn
newline (Pn f r _ i) = Pn f (r+1) 1 i
tab (Pn f r c i) = Pn f r (((c`div`8)+1)*8) i
-- | Add the given whitespace char to the given position.
-- Precondition: @white c | isSpace c = True@
white :: Char -> Posn -> Posn
white ' ' = addcol 1
white '\n' = newline
white '\r' = id
white '\t' = tab
white '\xa0' = addcol 1
white _ = error "precondition not satisfied: Posn.white c | isSpace c"