Add step proc for symbols

src/preserves.nim

@@ -273,6 +273,14 @@ func step*(pr, idx: Preserve): Option[Preserve] =
     if i < pr.len:
       result = some(pr[i])
 
+func step*[E](pr: Preserve[E]; key: Symbol): Option[Preserve[E]] =
+  ## Step into dictionary by a `Symbol` key.
+  if pr.isDictionary:
+    for (k, v) in pr.dict.items:
+      if k.isSymbol and k.symbol == key:
+        result = some(v)
+        break
+
 proc `[]=`*(pr: var Preserve; key, val: Preserve) =
   ## Insert `val` by `key` in the Preserves dictionary `pr`.
   for i in 0..pr.dict.high: