require $& for whitespace before or after a builder

make-pages/BuilderQQ.hs

@@ -18,9 +18,15 @@ import Data.List.NonEmpty (NonEmpty, toList)
 
 data Chunk = Lit String | Var String
 
+
+-- |
+-- * use @$var@ to insert a variable (instance of 'CanBuild')
+-- * use @$&@ to insert nothing like @\&@ in a string (e.g. to add whitespace
+--   at the start or end, or to have a variable followed by a letter
+-- * use @$$@ for a literal @$@
 parseB :: String -> ExpQ
 parseB = toExpQ . reverse . go "" [] . trim where
-  trim = dropWhileEnd isSpace . dropWhile (== '\n')
+  trim = dropWhileEnd isSpace . dropWhile isSpace
   go acc cs []             = addLit acc cs
   go acc cs ('$':'&':rest) = go acc cs rest         -- $&: expands to nothing
   go acc cs ('$':'$':rest) = go ('$' : acc) cs rest -- $$: expands to one $