Add located combinator; improved anchor matches with tests

src/Lexer.hs

@@ -175,22 +175,26 @@ anchors = do
   where
     anchor' = (string "#" <|> string "\\#")
 
+located :: Parser a -> Parser (SourcePos, a)
+located p = (,) <$> getPosition <*> p
+
+startPosition :: Parser a -> Parser SourcePos
+startPosition = fmap fst . located
+
 -- "Module.Name"
 -- "Module.Name#anchor"
+-- "Module.Name\#anchor" -- this has been deprecated for 9 years, thanks Ben
 modules :: Lexer
 modules = do
-    pos <- getPosition
-    void $ char '"'
-    pos' <- getPosition
-    modName <- modId
+    startPos <- startPosition $ char '"'
+    (modPos, modName) <- located modId
     anch <- option [] do
-        pos'' <- getPosition
-        void $ try (string "#" <|> string "\\#")
-        a <- Text.pack <$> many (satisfy (\c -> c /= '"' && not (isSpace c)))
-        pure [(pos'', Anchor a)]
+        anchPos <- startPosition (string "#" <|> string' "\\#")
+        txt <- Text.pack <$> many (satisfy (\c -> c /= '"' && not (isSpace c)))
+        pure [(anchPos, Anchor txt)]
 
     void $ char '"'
-    pure $ [(pos, Module), (pos', Token modName)] <> anch
+    pure $ [(startPos, Module), (modPos, Token modName)] <> anch
   where
     modId = intercalate "." <$> (fmap Text.pack <$> (conId `sepBy1` (char '.')))