Reading Musi code

Start by looking for names. A name is the handle you grab before reading the whole body.

let option := import "@std/option";
let Option := option.Option;

let Receipt := data {
  | Receipt(table : Int, total : Int)
};

let emptyReceipt := option.noneOf[Receipt]();

export let receiptForTable (table : Int) : Option[Receipt] :=
  option.someOf[Receipt](.Receipt(table := table, total := 0));

Scan names before details

Look for let, export let, and import. These forms tell you what the file gives to itself or to other files.

Do not start by reading every symbol. First make a map in your head. It is like reading street signs before choosing a route.

Read bodies after names

After you know the names, read the bodies. The body after := tells you how the value is made.

Reading order

Start with names, then operators, then calls.

let port := 8080;
let valid := port >= 1024 and port <= 65535;

port has the value 8080. >= checks the lower bound. <= checks the upper bound. and requires both checks.

Parenthesized expressions

A sequence expression is a parenthesized group of expressions. The final expression is the value of the sequence.

let message := (
  let port := 8080;
  "port ready"
);

Read the sequence as a small nested expression.