name: genericClosure args: [attrset]

Take an attrset with values named startSet and operator in order to return a list of attrsets by starting with the startSet and recursively applying the operator function to each item. The attrsets in the startSet and the attrsets produced by operator must contain a value named key which is comparable. The result is produced by calling operator for each item with a value for key that has not been called yet including newly produced items. The function terminates when no new items are produced. The resulting list of attrsets contains only attrsets with a unique key. For example,

builtins.genericClosure {
  startSet = [ {key = 5;} ];
  operator = item: [{
    key = if (item.key / 2 ) * 2 == item.key
         then item.key / 2
         else 3 * item.key + 1;
  }];
}

evaluates to

[ { key = 5; } { key = 16; } { key = 8; } { key = 4; } { key = 2; } { key = 1; } ]