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Getting Started

This short guide walks through writing and running a minimal Branchline transform.

Write your first transform

Create a file hello.bl with the following contents:

TRANSFORM Hello {
    LET greet = "Hello, " + input.name;
    OUTPUT { greeting: greet };
}

The transform reads the implicit input record, builds a new field, and emits it with OUTPUT.

Run the transform

You can execute Branchline from Kotlin using the test utility compileAndRun:

val result = compileAndRun(
    body = """
        LET greet = \"Hello, \" + input.name;
        OUTPUT { greeting: greet };
    """.trimIndent(),
    input = mapOf("name" to "Branchline")
)
println(result) // {greeting=Hello, Branchline}

The helper compiles the snippet and runs it against the provided input map.

Try it in the playground

Open the playground with the starter example preloaded: customer-profile.

Expected output for the starter example: 

{
  "id": 42,
  "full_name": "Ada Lovelace",
  "loyalty_tier": "standard",
  "shipping_city": "London"
}

Change the input JSON and rerun to see the output update. Enable tracing to view EXPLAIN provenance for variables you care about.

Next steps

  • Edit the program to add a field (e.g., loyalty tier label) and confirm the output changes.
  • Switch the input format to XML in the playground and try the junit-badge-summary example to see XML parsing.
  • Read the Language Overview for syntax details and explore the stdlib pages linked to interactive examples.