Ranges describe a span of values. They appear anywhere a program talks about positions, dates, seats, pages, ages, or levels.

let closed := 0..10;
let halfOpen := 0..<10;
halfOpen;

A range is more than two endpoints. The program also needs to know whether the endpoints are included and how values move from one point to the next.

Real-world spans

A classroom may use seat numbers 1 through 30. A calendar may use the days from Monday to Friday. A game may allow levels 1 through 10. Ranges make those shapes visible instead of scattering boundary checks.

Boundaries need names

When a range encodes policy, name the endpoints. adultAgeMinimum is easier to audit than a raw 18, and lastPublicPage is clearer than a number buried inside a comparison.

Core forms are the small hand tools of the language. Literals are raw materials, calls ask for work, operators join values, ranges mark spans, and lambdas carry a small action around. Each form should feel boring before you rely on it inside larger data or effect code.

When a core form feels hard, place it in a plain story. A ticket price plus a fee, a room number in a range, a message sent through a callable, or a small action saved as a lambda is enough. The syntax matters because it keeps that story exact.