Implement set with HashSet rather than CountTable

I didn't know HashSet was a thing.

src/preserves.nim

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: ISC
 
-import base64, endians, json, hashes, tables, streams
+import base64, endians, json, hashes, sets, streams, tables
 import bigints
 
 type
@@ -33,7 +33,7 @@ type
     of pkSequence:
       seq*: seq[Preserve[T]]
     of pkSet:
-      set*: CountTable[Preserve[T]]
+      set*: HashSet[Preserve[T]]
     of pkDictionary:
       dict*: Table[Preserve[T], Preserve[T]]
     of pkEmbedded:
@@ -76,7 +76,7 @@ proc `$`*[T](prs: Preserve[T]): string =
     result.add(']')
   of pkSet:
     result.add("#{")
-    for val in prs.set.keys:
+    for val in prs.set:
       result.add($val)
       result.add(' ')
     if result.len > 1:
@@ -208,10 +208,10 @@ proc `==`*[T](x, y: Preserve[T]): bool =
         if y.seq[i] != val: return false
       result = true
     of pkSet:
-      for val in x.set.keys:
-        if not y.set.hasKey(val): return false
-      for val in y.set.keys:
-        if not x.set.hasKey(val): return false
+      for val in x.set:
+        if not y.set.contains(val): return false
+      for val in y.set:
+        if not x.set.contains(val): return false
       result = true
     of pkDictionary:
       for (key, val) in x.dict.pairs:
@@ -248,7 +248,7 @@ proc hash*[T](prs: Preserve[T]): Hash =
     for val in prs.seq:
       h = h !& hash(val)
   of pkSet:
-    for val in prs.set.keys:
+    for val in prs.set:
       h = h !& hash(val)
   of pkDictionary:
     for (key, val) in prs.dict.pairs:
@@ -359,8 +359,8 @@ proc write*[T](str: Stream; prs: Preserve[T]) =
     str.write(0x84'u8)
   of pkSet:
     str.write(0xb6'u8)
-    for key in prs.set.keys:
-      str.write(key)
+    for val in prs.set.items:
+      str.write(val)
     str.write(0x84'u8)
   of pkDictionary:
     str.write(0xb7'u8)
@@ -423,8 +423,8 @@ proc parsePreserve*(s: Stream): Preserve[void] =
   of 0xb6:
     result = Preserve[void](kind: pkSet)
     while s.peekUint8() != endMarker:
-      let key = s.parsePreserve()
-      result.set[key] = 0
+      let val = s.parsePreserve()
+      result.set.incl(val)
     discard s.readUint8()
   of 0xb7:
     result = Preserve[void](kind: pkDictionary)