roc/crates/cli_testing_examples/platform-switching/README.md
2022-09-11 22:32:15 -06:00

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# Platform switching
To run, `cd` into this directory and run this in your terminal:
```bash
roc run
```
This will run `main.roc` because, unless you explicitly give it a filename, `roc run`
defaults to running a file named `main.roc`. Other `roc` commands (like `roc build`, `roc test`, and so on) also default to `main.roc` unless you explicitly give them a filename.
## About this example
This uses a very simple platform which does nothing more than printing the string you give it.
The line `main = "Which platform am I running on now?\n"` sets this string to be `"Which platform am I running on now?"` with a newline at the end, and the lines `packages { pf: "c-platform/main.roc" }` and `provides [main] to pf` specify that the `c-platform/` directory contains this app's platform.
This platform is called `c-platform` because its lower-level code is written in C. There's also a `rust-platform`, `zig-platform`, and so on; if you like, you can try switching `pf: "c-platform/main.roc"` to `pf: "zig-platform/main.roc"` or `pf: "rust-platform/main.roc"` to try one of those platforms instead. They all do similar things, so the application won't look any different.
If you want to start building your own platforms, these are some very simple example platforms to use as starting points.