Sesi Language | Syntax and Examples

Interactive Tour

Learn the language, not the ceremony

Sesi keeps fundamentals crisp: values, logic, functions, and structured control flow.

conditions.sesi

let score = 92let passingGrade = 70if score >= passingGrade {  show "Status: You passed with distinction!"} else {  show "Status: Needs improvement"}

let colors = ["violet", "cyan", "emerald", "amber"]for item in colors {  show "Palette token ->" item}

let response = web_get("https://api.github.com/zen")show "Design principle: " response

allow "std/db" in with {db_open}let db = db_open("app.db")let users = db.collection("users")users.insert({"name": "Alex", "role": "Developer"})show users.find({"name": "Alex"})

Live Simulated Output

Status: You passed with distinction!

Language foundations

The pieces fit together quickly.

Sesi uses a compact set of readable forms. Learn values, functions, collections, and control flow, then compose them into larger programs.

Practice in the syntax demo

Values

Bind with `let`

Create named values without declaration ceremony. Sesi infers the type when an annotation is not needed.

let name = "Sesi"

Functions

Define focused behavior

Functions accept typed parameters, can declare a return type, and keep reusable logic close to its intent.

fn double(n: number) -> number

Control flow

Branch without noise

Conditions use readable expressions and braces. The structure stays visible without punctuation at every line.

if ready { show "go" }

Collections

Iterate directly

Arrays and objects are ordinary values. Walk a collection with a direct for … in loop.

for item in items { … }

Output

Say it with `show`

Place strings and values next to each other. Output reads naturally without manual concatenation.

show "Hello," name

Capabilities

Allow what a file uses

Bring module capabilities into scope explicitly so system access is visible at the top of the program.

allow "std/db" in with {db_open}

A complete program

Readable from top to bottom.

A Sesi file can declare its capabilities, define reusable behavior, and execute top-level statements without a required application wrapper.

report.sesione file · one command

let scores = [92, 78, 88]fn average(values) {  let total = 0  for value in values {    total = total + value  }  return total / len(values)}show "Class average:" average(scores)

Class average: 86Exit Code: 0

From source to output

Run Sesi your way.

Use a file for a program, evaluate a quick expression, or work interactively in the browser syntax demo.

Run a file

Execute a complete .sesi program from the command line.

$ sesi app.sesi

Evaluate a line

Check a small expression without creating a source file.

$ sesi -e "show 'hello'"

Try the syntax

Edit examples and inspect simulated output directly in the browser.

Open syntax demo

Go further

Start with the core. Add capabilities as the program grows.

Install Sesi locally or explore how optional reasoning fits into an otherwise standard program.

Install Sesi Optional reasoning