Store a function instead of a Boolean

Instead of storing isDisplay and then always choosing displayMath or math
based on that, just store displayMath or math directly.

src/Text/Pandoc/Readers/HTML.hs

@@ -927,25 +927,21 @@ pMath inCase = try $ do
   let attr = toStringAttr attr'
   unless inCase $
     guard (maybe True (== mathMLNamespace) (lookup "xmlns" attr))
-  let isDisplay = case lookup "display" attr of
-                     Just "block" -> True
-                     _ -> False
+  let constructor = case lookup "display" attr of
+                       Just "block" -> B.displayMath
+                       _ -> B.math
   contents <- manyTill pAny (pSatisfy (matchTagClose "math"))
   -- KaTeX and others include original TeX in annotation tag;
   -- just use this if present rather than parsing MathML:
   case extractTeXAnnotation contents of
-    Just x -> return $ if isDisplay
-                          then B.displayMath x
-                          else B.math x
+    Just x -> return $ constructor x
     Nothing ->
       case mathMLToTeXMath (renderTags $
               [open] <> contents <> [TagClose "math"]) of
            Left _   -> return $ B.spanWith ("",["math"],attr) $ B.text $
                                  innerText contents
            Right "" -> return mempty
-           Right x  -> return $ if isDisplay
-                                   then B.displayMath x
-                                   else B.math x
+           Right x  -> return $ constructor x
 
 extractTeXAnnotation :: [Tag Text] -> Maybe Text
 extractTeXAnnotation [] = Nothing