Escape | as \vert in LaTeX math.

This avoids a clash with highlighting-kate's macros, which
redefine | as a short verbatim delimiter.  Thanks to
Björn Peemöller for raising this issue.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -214,6 +214,13 @@ stringToLaTeX  isUrl (x:xs) = do
        '\x2013' | ligatures -> "--" ++ rest
        _        -> x : rest
 
+-- This is needed because | in math mode interacts badly with
+-- highlighting-kate, which redefines | as a short verb command.
+escapeMath :: String -> String
+escapeMath ('|':xs) = "\\vert " ++ escapeMath xs
+escapeMath (x:xs)   = x : escapeMath xs
+escapeMath []       = ""
+
 -- | Puts contents into LaTeX command.
 inCmd :: String -> Doc -> Doc
 inCmd cmd contents = char '\\' <> text cmd <> braces contents
@@ -603,8 +610,10 @@ inlineToLaTeX (Quoted qt lst) = do
                       then char '`' <> inner <> char '\''
                       else char '\x2018' <> inner <> char '\x2019'
 inlineToLaTeX (Str str) = liftM text $ stringToLaTeX False str
-inlineToLaTeX (Math InlineMath str) = return $ char '$' <> text str <> char '$'
-inlineToLaTeX (Math DisplayMath str) = return $ "\\[" <> text str <> "\\]"
+inlineToLaTeX (Math InlineMath str) =
+  return $ char '$' <> text (escapeMath str) <> char '$'
+inlineToLaTeX (Math DisplayMath str) =
+  return $ "\\[" <> text (escapeMath str) <> "\\]"
 inlineToLaTeX (RawInline "latex" str) = return $ text str
 inlineToLaTeX (RawInline "tex" str) = return $ text str
 inlineToLaTeX (RawInline _ _) = return empty

tests/Tests/Writers/LaTeX.hs

@@ -32,4 +32,8 @@ tests = [ testGroup "code blocks"
           [ "in footnotes" =: note (para "hi" <> codeBlock "hi") =?>
             "\\footnote{hi\n\n\\begin{Verbatim}\nhi\n\\end{Verbatim}\n}"
           ]
+        , testGroup "math"
+          [ "escape |" =: para (math "\\sigma|_{\\{x\\}}") =?>
+            "$\\sigma\\vert _{\\{x\\}}$"
+          ]
         ]