You are currently looking at the < v8.2.0 docs (Reason v3.6 syntax edition). You can find the latest manual page here.
(These docs cover all versions between v3 to v8 and are equivalent to the old BuckleScript docs before the rebrand)
Build System Overview
ReScript comes with a build system, bsb, that's meant to be fast, lean and used as the authoritative build system of the community.
Bsb provides a few templates to quickly start a new project:
bsb -init my-directory-name
Feel free to inspect the various files in the newly generated directory. To see all the templates available, do:
The build description file is called
bsconfig.json. Every ReScript project needs one.
To build a project, run:
-w to keep the built-in watcher running. Any new file change will be picked up and the build will re-run.
Note: third-party libraries (in
node_modules) aren't watched, as doing so may exceed the node.js watcher count limit. If you're doing quick and dirty modifications inside
node_modules, you have to do
bsb -clean-world -make-world to rebuild them.
Note 3: If you are developing across multiple devices, you may find the
-ws configuration useful in order to have live-reloading across the network. Possible configurations are:
bsb -make-world -w -ws _(default)
bsb -make-world -w -ws 0.0.0.0:9999
bsb -make-world -w -ws 5000
To build only yourself, use
bsb -help to see all the available options.
If you ever get into a stable build for edge-case reasons, use:
bsb -clean to clean only your own artifacts.
Bsb generates a
.merlin file, used by various editor plugins under the hood to power e.g. autocomplete, type hint, diagnosis, etc.
A typical problem with traditional build systems is that they're not resilient against the user moving/deleting source files. Most don't clean up the old artifacts correctly after such user action*. Bsb is unfortunately no different, unless you turn on
"suffix": ".bs.js" in
bsconfig.json, in which case we can track which JS artifact belongs to which source file correctly, even against source file moving/deletion.
* One such build system that tracks these correctly & efficiently is Tup. See the (rather accessible!) paper here. Unfortunately, Tup's implementation uses FUSE and other systems, which we can't safely use on every platform.