It is mentioned prominently enough in the readme, I would say. 2²⁶ is plenty enough for many applications. I currently use a persistent intmap to label continuations in a toy CPS compiler, and with my current approach there is no chance whatsoever that any conceivable program would compile to use that many continuation labels.

This limit comes from using int32s. Does anyone have an idea why on modern machines it isn't making use of int64s?