Your first program

By the end of this page, you will have a program that prints a greeting and an executable you can run yourself. You need a text editor, a terminal, and Dodo with a C toolchain installed. No prior knowledge of borrowing or systems programming is required.

Commands go in your terminal. Dodo code goes in a .dodo file. The examples use Linux shell commands unless a PowerShell version is shown; dodo commands work in either shell.

1. Create a project folder

Create an empty folder and enter it:

mkdir hello
cd hello

Save the following as main.dodo inside hello. Check that your editor has not added .txt to the filename. A project needs no manifest or package manager.

package main

import "std/console"

fn main() {
    console.println("Hello, world!")!
}

Your folder now contains:

hello/
  main.dodo

2. Run it

From the terminal in hello, run:

dodo run

Expected output:

Hello, world!

The compiler first checks your source, creates a temporary executable, and runs it. When the program finishes, you return to the terminal prompt. There is no separate install step for std/console: it is bundled with Dodo.

If the terminal cannot find dodo, revisit installation. If the compiler cannot execute cc, configure the C toolchain. If it cannot find main.dodo, open the terminal in the folder containing your source.

3. Understand each line

Printing can fail, for example when an output pipe is closed. Its Result reports either the byte count or an I/O error. The final ! explicitly chooses to stop on an error for this first example. Later, you will use match and ? to recover or pass an error to a caller. The exclamation mark inside the greeting is just printed text.

A newline ends each statement here; semicolons are optional. Reaching the end of this main returns success, exit status 0. That status is not printed. To see it immediately after a run, use echo $? on Linux or $LASTEXITCODE in PowerShell.

4. Change the program

Replace the complete contents of main.dodo with:

package main

import "std/console"

fn main() {
    let name = "Dodo"
    let lessons = 3i32
    console.printf("Hello, {}!\n", name)!
    console.printf("{} lessons to try.\n", lessons)!
}

Run dodo run again. It prints:

Hello, Dodo!
3 lessons to try.

let gives a value a name without allowing reassignment. 3i32 is the integer 3 with a signed 32-bit type. Each {} in a literal format is replaced by the corresponding argument. \n is a newline; printf adds only the characters you request. The compiler checks the literal format and its arguments.

Try it: change the name and lesson count, then run again. Remove the second argument from one printf call and run dodo check to see the diagnostic. Restore the argument before continuing.

5. Check and format

These commands do different jobs:

dodo check
dodo fmt
dodo check

check verifies syntax, types, ownership, and borrowing without running the program or invoking the linker. A successful check prints Checked main.dodo. fmt rewrites source with consistent formatting. Save your editor changes before running commands so they use the current file.

A successful check cannot predict every runtime failure. Index bounds, integer overflow, and failures reported by library calls still matter when a program runs.

6. Keep an executable

run removes its temporary executable afterward. Use compile when you want a file to keep. On Linux:

dodo compile
./build/hello

The default name comes from the project folder. On Windows, choose an explicit .exe path and run it with PowerShell:

dodo compile -o build/hello.exe
.\build\hello.exe

Both commands run your program again. You do not need Dodo to launch the resulting executable, but its platform runtime and any libraries you linked must be available. The command-line guide explains output names, optimization, debugging, and target selection.

Next steps

Continue with variables, values, and expressions, then types and functions. The temperature report walkthrough combines these ideas in one complete program. Editor setup adds diagnostics and completion as you type; console I/O extends printing to input and stderr.