added json.hash

lib/pure/json.nim

@@ -620,6 +620,7 @@ proc `%`*(elements: openArray[PJsonNode]): PJsonNode =
   for i, p in pairs(elements): result.elems[i] = p
 
 proc `==`* (a,b: PJsonNode): bool =
+  ## Check two nodes for equality
   if a.kind != b.kind: false
   else:
     case a.kind
@@ -638,6 +639,24 @@ proc `==`* (a,b: PJsonNode): bool =
     of JObject:
       a.fields == b.fields
 
+proc hash* (n:PJsonNode): THash =
+  ## Compute the hash for a JSON node
+  case n.kind
+  of jArray:
+    result = hash(n.elems)
+  of jObject:
+    result = hash(n.fields)
+  of jInt:
+    result = hash(n.num)
+  of jFloat:
+    result = hash(n.fnum)
+  of jBool:
+    result = hash(n.bval.int)
+  of jString:
+    result = hash(n.str)
+  of jNull:
+    result = hash(0)
+
 proc len*(n: PJsonNode): int = 
   ## If `n` is a `JArray`, it returns the number of elements.
   ## If `n` is a `JObject`, it returns the number of pairs.