| Both the synchronous and asynchronous frontends preserve as much state as possible (all untouched modules are kept). They differ in the control flow they permit (the asynchronous one being more expressive). I will try to make a parallel with a simple Makefile-driven project. In the initial build, all files are built, following a topological ordering of the dependencies.
For the Makefile it means invoking some unix command for each intermediate artefact.
For Hotcaml, it means parsing, typing, compiling and loading each module. After that, build is incremental: when a file is modified, only this file and its reverse dependencies need to be rebuilt.
Make will keep the existing artifacts that are not out of date.
Hotcaml will keep the existing modules that are not out of date. And their state is preserved. Now, the synchronous frontend is quite like a regular Makefile: a build step is considered done when the build command finishes.
The asynchronous frontend allows command to run in the background, like a Makefile that would spawn processes/daemon using the shell & control operator. In Hotcaml, these threads continue executing concurrently with the reloading process. They can be notified that their "host" module has been reloaded by registering with some runtime service (via a module named Hotlink). |