What happened

Converting a Seq to a list on anything remotely large (even a Seq with 1000 items seems to be enough) causes a max call size exceeded error.

After tracing through the code a bit, it seems to be happening because the implementation of flatDeep is unnecessarily recursive (it iterates recursively in the default case).

How to reproduce

This codesandbox repros the issue: https://codesandbox.io/s/stoic-brook-zlzcs6?file=/src/index.js