Blocks

In Stylus (in JavaScript) blocks in arrays are processed via

for (block.index = 0; block.index < block.nodes.length; ++block.index) {
  block.nodes[block.index] = this.visit(block.nodes[block.index]);
}

But when a mixin is visited, the block.index is set to 0 and the block is not updated.

In Stilus (Python) such a system is not possible; but a mixin attribute is used instead.

Both systems are ugly.