Execution takes far more time than it should

porting this issue over from [AREPL](https://github.com/Almenon/AREPL/issues/41)

```python
x = [[i for i in range(10000000)]]
```
Timings in ms:

List Size | Python Time | Total Time (py & JS)
------------ | ------------ | -------------
10^4 | 0 | 23
10^5 | 2.98 | 225
10^6 | 48.1 | 2363
10^7 | 489 | 24337

I'd be okay with a doubling or even tripling of the execution time but this is clearly rediculous. Only **~2%** of the execution time is actually spent executing the user's code. God knows what the computer is doing the rest of the time. Sipping martinis on the beach? 🏖️ 🍸