Fixed wrapped exception handling

private/json.nim

@@ -206,9 +206,9 @@ proc loadToJson*(s: Stream): seq[JsonNode] =
         raise e
     except YamlConstructionStreamError:
         let e = getCurrentException()
-        if e.parent is IOError:
+        if e.parent of IOError:
             raise cast[ref IOError](e.parent)
-        elif e.parent is YamlParserError:
+        elif e.parent of YamlParserError:
             raise cast[ref YamlParserError](e.parent)
         else:
             # can never happen

private/presenter.nim

@@ -4,6 +4,8 @@
 #    See the file "copying.txt", included in this
 #    distribution, for details about the copyright.
 
+import typetraits
+
 type
     DumperState = enum
         dBlockExplicitMapKey, dBlockImplicitMapKey, dBlockMapValue,
@@ -499,9 +501,9 @@ proc transform*(input: Stream, output: Stream, style: PresentationStyle,
             present(events, output, tagLib, style, indentationStep)
     except YamlPresenterStreamError:
         let e = getCurrentException()
-        if e.parent is IOError:
+        if e.parent of IOError:
             raise cast[ref IOError](e.parent)
-        elif e.parent is YamlParserError:
+        elif e.parent of YamlParserError:
             raise cast[ref YamlParserError](e.parent)
         else:
             # never happens

yaml/serialization.nim

@@ -484,9 +484,9 @@ proc load*[K](input: Stream, target: var K)
         raise
     except YamlConstructionStreamError:
         let e = cast[ref YamlConstructionError](getCurrentException())
-        if e.parent is IOError:
+        if e.parent of IOError:
             raise cast[ref IOError](e.parent)
-        elif e.parent is YamlParserError:
+        elif e.parent of YamlParserError:
             raise cast[ref YamlParserError](e.parent)
         else:
             assert(false)