From 7ec778d74756c7a7481e29762a03128e79ec6070 Mon Sep 17 00:00:00 2001
From: aarne <aarne@chalmers.se>
Date: Fri, 17 Oct 2014 06:40:06 +0000
Subject: [PATCH] lexer for latex code: don't separate backslash from the macro
 name that it marks

---
 src/runtime/haskell/PGF/Lexing.hs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/runtime/haskell/PGF/Lexing.hs b/src/runtime/haskell/PGF/Lexing.hs
index 782757b03..d5286a478 100644
--- a/src/runtime/haskell/PGF/Lexing.hs
+++ b/src/runtime/haskell/PGF/Lexing.hs
@@ -54,6 +54,16 @@ unlexCode s = case s of
   _ -> []
 
 
+-- | LaTeX lexer in the math mode: \ should not be separated from the next word
+
+lexLatexCode :: String -> [String]
+lexLatexCode = restoreBackslash . lexCode where --- quick hack: postprocess Haskell's lex
+  restoreBackslash ws = case ws of
+    "\\":"\\":ww -> "\\\\":restoreBackslash ww
+    "\\":w:ww -> ("\\" ++ w) : restoreBackslash ww
+    w:ww -> w:restoreBackslash ww
+    _ -> ws
+
 -- * Mixed lexing
 
 -- | LaTeX style lexer, with "math" environment using Code between $...$
@@ -64,7 +74,7 @@ lexMixed = concat . alternate False where
       (t,[])  -> lex env t : []
       (t,c:m) -> lex env t : [[c]] : alternate (not env) m
     _ -> []
-  lex env = if env then lexCode else lexText
+  lex env = if env then lexLatexCode else lexText
 
 unlexMixed :: [String] -> String
 unlexMixed = capitInit . concat . alternate False where