1. Run something real

Over this tutorial you build metrics: a tiny pipeline that reads a batch of raw event lines, parses and validates each one, and prints a per-user report. Every page adds one stage, and the interesting part is that the data's shape changes as it moves through — which is where Metel's records, row bounds, and ownership rules earn their place.

This page: get the interpreter running and walk the batch.

The entry point

Every program starts in main. Put this in metrics.mtl:

fun main() {
    let raw := [
        "7 click /home",
        "7 buy 42",
        "3 click /docs",
    ];

    var line := 0;
    for (text in raw) {
        line := line + 1;
        println("${line}: ${text}");
    }
}

Run it:

cargo run -- metrics.mtl

1: 7 click /home
2: 7 buy 42
3: 3 click /docs

A few things this already shows:

• let binds a value; var binds one you can reassign (line := line + 1). A plain let binding cannot be reassigned.
• [ … ] is an array literal. for (text in raw) walks it.
• ${…} interpolates any value with a .to_string() — every built-in scalar has one.

Each raw line is "<user> <kind> <arg>": a click carries a path, a buy carries an amount.

By the end you'll have

A program that iterates the event batch and prints each line with its number.

Next: Give the data a shape — turn each line into something with named fields, without declaring a type for it.