Your First Program

Now that you've set up your starter Claro project in the previous section, let's go through the process of implementing your first program!

Create hello_world.claro

Fig 1:

print("Hello, world!");

Hello World is a one-liner in Claro, so it's a great place to start learning how to declare a new Claro program using Bazel. Just to keep things simple, copy the above line into a new file at //example/hello_world.claro.

Fig 2:

|-- .bazelrc
|-- .bazelversion
|-- MODULE.bazel
`-- example
    |-- BUILD
    |-- demo.claro
    |-- hello_world.claro
    `-- input.txt

1 directory, 8 files

Declare a New claro_binary(...) Target in Your BUILD File

Now, we'll simply add a new build target for our Hello World program to the existing BUILD file that was generated as part of the starter project.

Fig 3:

load("@claro-lang//:rules.bzl", "claro_binary")

  name = "demo_bin",
  main_file = "demo.claro",
  resources = {
    "Input": "input.txt",

  name = "hello_world",
  main_file = "hello_world.claro",

Now Execute Your Program!

That's all there is to it! Now you can use the following command to have Bazel build and then run your program:

Note: The below recording was made with asciinema - try pausing and copying any text.

Congratulations! You just wrote and executed your first Claro program entirely from scratch!

Avoiding Bazel's Extra Output

Notice that when you used bazel run ... to run your executable build target, Bazel produced a bunch of INFO: ... logs related to the build process. Since the program built successfully, this is something that you can usually just ignore. However, if this extra noise bothers you, you can make use of Bazel's generated build artifacts to run the program directly, without any of Bazel's extra logging. Notice the very last line in Bazel's output:

INFO: Running command line: bazel-bin/example/hello_world

This is a script that can be directly invoked to run the built executable program locally.

This is not a portable executable! Continue reading to learn how to generate a portable executable.

Note: The below recording was made with asciinema - try pausing and copying any text.

Generating a Portable Executable ("Deploy Jar")

As Claro is a JVM language, you can easily generate a self-contained Jar file that can be run anywhere that a JVM is installed. Generate the "Deploy Jar" by appending _deploy.jar to the end of any claro_binary() build target, and can then run it using java -jar ... as you would any executable Jar:

Note: The below recording was made with asciinema - try pausing and copying any text.

Warning: The `java -jar ...` command demonstrated above will make use of your local Java installation. Assuming that you've kept the flag `common --java_runtime_version=remotejdk_11` in your .bazelrc as described in the previous section, you may have been running Claro programs without even manually installing Java, meaning that this command will fail. Generally speaking, you shouldn't worry about this as it's encouraged to use `bazel run ...` during local development anyway.