The Bosque paper says the following:

> JavaScript took an interesting step by decoupling the core compute language in the JS specification from the IO and event loop which are provided by the host [...]. We take the same approach of decoupling the core compute language, BOSQUE, from the host runtime which is responsible for managing environmental interaction.

So it seems that Bosque doesn't do IO directly, but instead specifies how a given input is mapped to some output.