Be more consistent about sorting dictionary keys

src/preserves.nim

@@ -195,7 +195,8 @@ proc `<`*[A, B](x: Preserve[A]; y: Preserve[B]): bool =
       when (not A is void) and (A is B):
         result = x.embed < y.embed
 
-proc cmp*[E](x, y: var Preserve[E]): int =
+func cmp*[E](x, y: Preserve[E]): int =
+  ## Compare by Preserves total ordering.
   if x == y: 0
   elif x < y: -1
   else: 1
@@ -203,6 +204,10 @@ proc cmp*[E](x, y: var Preserve[E]): int =
 proc sort*[E](pr: var Preserve[E]) = sort(pr.sequence, cmp)
   ## Sort a Preserves array by total ordering.
 
+proc sortDict[E](pr: var Preserve[E]) =
+  sort(pr.dict) do (x, y: DictEntry[E]) -> int:
+    cmp(x.key, y.key)
+
 proc cannonicalize*[E](pr: var Preserve[E]) {.gcsafe.} =
   ## Cannonicalize a compound Preserves value by total ordering.
   case pr.kind
@@ -214,8 +219,7 @@ proc cannonicalize*[E](pr: var Preserve[E]) {.gcsafe.} =
   of pkDictionary:
     apply(pr.dict) do (e: var DictEntry[E]):
       cannonicalize(e.val)
-    sort(pr.dict) do (x, y: DictEntry[E]) -> int:
-      cmp(x.key, y.key)
+    sortDict(pr)
   else:
     discard
 
@@ -943,7 +947,7 @@ proc toPreserve*[T](x: T; E = void): Preserve[E] =
         var pr = fieldToPreserve(key, val)
         applyEmbed(key, pr)
         result[toSymbol(key, E)] = pr
-      cannonicalize(result)
+      sortDict(result)
     else:
       {.warning: "failed to preserve object " & $T .}
       result = toPreserveHook(x, E)
@@ -964,7 +968,7 @@ proc toPreserveHook*[A, B](table: Table[A, B]|TableRef[A, B], E: typedesc): Pres
   result = initDictionary(E)
   for k, v in table.pairs:
     result[toPreserve(k, E)] = toPreserve(v, E)
-  cannonicalize(result)
+  sortDict(result)
 
 func containsNativeEmbeds[E](pr: Preserve[E]): bool =
   ## Check if a `Preserve[E]` is convertible to `Preserve[void]`.