Running .mbtx Scripts

Running .mbtx Scripts#

The Moon build system lets you write script files in MoonBit without any module or package configuration files. Script files use the special .mbtx extension.

Run a .mbtx file#

Write a script script.mbtx:

///|
import {
  "moonbitlang/core/list" @ls
}

///|
async fn main {
  let xs = @ls.List(["1", "2", "3"])
  debug(xs)
}

Then run this script directly:

$ moon run script.mbtx

In .mbtx, you can declare imports at the top of the file using the same syntax as package configuration. There is one difference: import paths can optionally include a version @version after the module name:

///|
import {
  "moonbitlang/async@0.20.2/fs",
  "moonbitlang/async@0.20.2",
}

///|
async fn main {
  ...
}

All imported packages from the same module must use the same version.

If the import path is not explicitly versioned, it uses the latest version in the local registry index.

A script may add * after an import to bring all definitions from that package into its scope. The import may also set a custom package alias with @alias:

///|
import {
  "moonbitlang/core/queue" @q *
}

///|
fn main {
  let queue = Queue([1, 2, 3])
  println(queue.length())
  let qualified = @q.Queue([4, 5])
  println(qualified.length())
}

The package alias remains available, so the example can use both Queue and @q.Queue. Without an explicit @alias, the package's default alias is used. Import-all syntax is limited to .mbtx scripts; regular packages should use package aliases or using declarations. Prefer explicit imports when name conflicts would make a script difficult to read.

Test a .mbtx script#

Pass a script path to moon test to test that script by itself:

moon test script.mbtx

The script must define fn main, but the generated test entrypoint does not run it. An explicit .mbtx path selects only that script, even when it is inside a project; conversely, package-wide test runs do not include .mbtx scripts.

Run a .mbtx script from stdin#

Moon supports running a .mbtx script from stdin:

$ cat script.mbtx | moon run -

For short scripts, pass the .mbtx source directly with -c:

$ moon run -c "<script>"
$ moon run -c 'fn main { println("hello") }'

You can also use a heredoc, a feature provided by the shell:

$ moon run - <<EOF
fn main {
  println("hello")
}
EOF
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