More sophisticated flanking rules for math

commonmark-extensions/src/Commonmark/Extensions/Math.hs

@@ -15,11 +15,16 @@ import Commonmark.Html
 import Text.Parsec
 import Data.Text (Text)
 import qualified Data.Text as T
+import qualified Data.Map.Strict as M
 
 mathSpec :: (Monad m, IsBlock il bl, IsInline il, HasMath il)
          => SyntaxSpec m il bl
 mathSpec = mempty
   { syntaxInlineParsers = [withAttributes parseMath]
+  -- A very odd workaround. Is there a better way to:
+  -- 1. Get the precedingTokTypes map populated with info about '$'
+  -- 2. Have the math spans otherwise follow the same precedence as code spans, not emphasis
+  , syntaxFormattingSpecs = [FormattingSpec '$' False False Nothing Nothing '$']
   }
 
 class HasMath a where
@@ -38,13 +43,16 @@ instance (HasMath i, Monoid i) => HasMath (WithSourceMap i) where
 
 parseMath :: (Monad m, HasMath a) => InlineParser m a
 parseMath = try $ do
-  symbol '$'
+  Tok _ pos _ <- symbol '$'
   display <- (True <$ symbol '$') <|> (False <$ notFollowedBy whitespace)
   contents <- try $ untokenize <$> pDollarsMath 0
+  st <- getState
+  let isPrecededByWordChars = M.lookup pos (precedingTokTypes st) == Just WordChars
+  isFollowedByWordChars <- (==) WordChars . maybe LineEnd tokType <$> optionMaybe (lookAhead anyTok)
   let isWs c = c == ' ' || c == '\t' || c == '\r' || c == '\n'
   if display
      then displayMath contents <$ symbol '$'
-     else if T.null contents || isWs (T.last contents)
+     else if T.null contents || isWs (T.last contents) || isPrecededByWordChars || isFollowedByWordChars
              -- don't allow math to end with SPACE + $
              then mzero
              else return $ inlineMath contents

commonmark-extensions/test/math.md

@@ -87,3 +87,18 @@ $b<a>c$
 .
 <p><span class="math inline">\(b&lt;a&gt;c\)</span></p>
 ````````````````````````````````
+
+Inline math openers can't be immediately preceded by
+alphanumeric characters:
+```````````````````````````````` example
+Expect$Nothing$
+.
+<p>Expect$Nothing$</p>
+````````````````````````````````
+
+Or immediately followed by them:
+```````````````````````````````` example
+./install.sh $PLATFORM-$VERSION
+.
+<p>./install.sh $PLATFORM-$VERSION</p>
+````````````````````````````````

commonmark/src/Commonmark/Inlines.hs

@@ -26,6 +26,7 @@ module Commonmark.Inlines
   , pLinkTitle
   , pEscaped
   , pEscapedSymbol
+  , precedingTokTypes
   , processEmphasis
   , processBrackets
   , pBacktickSpan