Escape zero-length Symbols

src/preserves.nim

@@ -27,14 +27,16 @@ const
   compoundKinds* = {pkRecord, pkSequence, pkSet, pkDictionary}
 
 type Symbol* = distinct string
-proc `$`*(s: Symbol): string {.borrow.}
 proc `<`*(x, y: Symbol): bool {.borrow.}
 proc `==`*(x, y: Symbol): bool {.borrow.}
 proc hash*(s: Symbol): Hash {.borrow.}
 proc len*(s: Symbol): int {.borrow.}
 
+proc `$`*(s: Symbol): string =
+  if s.len == 0: "||" else: string(s)
+
 type
-  Preserve*[E = void] = object
+  Preserve*[E] = object
     embedded*: bool
       ## Flag to mark embedded Preserves
     case kind*: PreserveKind