Teach advanceSrcLoc about tab characters

[ghc-hetmet.git] / compiler / basicTypes / SrcLoc.lhs

diff --git a/compiler/basicTypes/SrcLoc.lhs b/compiler/basicTypes/SrcLoc.lhs
index 02c3e8a..e213bef 100644 (file)
--- a/compiler/basicTypes/SrcLoc.lhs
+++ b/compiler/basicTypes/SrcLoc.lhs
@@ -72,6 +72,8 @@ module SrcLoc (
 import Util
 import Outputable
 import FastString
+
+import Data.Bits
 \end{code}
 
 %************************************************************************
@@ -87,10 +89,7 @@ this is the obvious stuff:
 data SrcLoc
   = SrcLoc     FastString      -- A precise location (file name)
                {-# UNPACK #-} !Int             -- line number, begins at 1
-               {-# UNPACK #-} !Int             -- column number, begins at 0
-               -- Don't ask me why lines start at 1 and columns start at
-               -- zero.  That's just the way it is, so there.  --SDM
-
+               {-# UNPACK #-} !Int             -- column number, begins at 1
   | UnhelpfulLoc FastString    -- Just a general indication
 \end{code}
 
@@ -134,12 +133,15 @@ srcLocCol :: SrcLoc -> Int
 srcLocCol (SrcLoc _ _ c) = c
 srcLocCol _other         = panic "srcLocCol: unknown col"
 
--- | Move the 'SrcLoc' down by one line if the character is a newline
--- and across by one character in any other case
+-- | Move the 'SrcLoc' down by one line if the character is a newline,
+-- to the next 8-char tabstop if it is a tab, and across by one
+-- character in any other case
 advanceSrcLoc :: SrcLoc -> Char -> SrcLoc
-advanceSrcLoc (SrcLoc f l _) '\n' = SrcLoc f  (l + 1) 0
+advanceSrcLoc (SrcLoc f l _) '\n' = SrcLoc f  (l + 1) 1
+advanceSrcLoc (SrcLoc f l c) '\t' = SrcLoc f  l ((((c `shiftR` 3) + 1)
+                                                  `shiftL` 3) + 1)
 advanceSrcLoc (SrcLoc f l c) _    = SrcLoc f  l (c + 1)
-advanceSrcLoc loc           _    = loc -- Better than nothing
+advanceSrcLoc loc            _    = loc -- Better than nothing
 \end{code}
 
 %************************************************************************