This comes with a bit of last mile issue, if just chatting with GPT in the chat panel and keep steering it, it's generally fine (as a power user).

But when building it in a tool that serve end users, we are starting to see that a 80% success rate in generating good looking charts can become a big issue. We experienced this when building some data analysis system. So the reliability, expressiveness, and costs (in terms of time and tokens) are hard to achieve all together with directly generating matplotlib, vega-lite etc.

So we essentially designed the langauge as a trade-off across the three, by moving some decisions to the compiler to reduce generation cost while maintain good expressivenss.