Getting started

In this chapter you install Cromo, write your first program, and meet cromo, the command that builds, runs, tests and formats Cromo code.

#Installation

Cromo is installed for your user, without administrator rights, with one line. On Windows, in PowerShell:

irm https://cromolang.org/install.ps1 | iex

On Linux:

curl -sSf https://cromolang.org/install.sh | sh

The script downloads the archive of the latest version, checks its SHA-256, and unpacks it in ~/.cromo (%USERPROFILE%\.cromo on Windows). It adds ~/.cromo/current/bin to the PATH and, if it finds Visual Studio Code, installs the Cromo extension. Open a new terminal, then check the installation:

cromo version

cromo 0.27.1 (LLVM 23.1.4)

That is all. cromo contains the compiler and the linker: it needs no C compiler, no Visual Studio and no Windows SDK, and the programs it writes do not depend on the C runtime of the system.

Note: the archive can also be installed by hand: download it from cromolang.org, unpack it anywhere and add its bin folder to the PATH. cromo finds the library in the lib folder next to bin.

#Hello, world!

Create a folder for your programs and, in it, a file named hello.cro:

i32 main() {
    println("Hello, world!")
    ret 0
}

Then run it:

cromo run hello.cro

Hello, world!

Let us look at the program:

• i32 main() declares the function main, where every program starts. The type comes before the name, as in C: main returns an i32, a 32-bit integer, which becomes the exit code of the program.
• println prints a line. Its first argument is a format string, which can contain {} for the values that follow it: println("{} + {} = {}", a, b, a + b).
• ret returns from a function. Cromo writes ret where C writes return.
• There are no semicolons: a statement ends at the end of its line.

A main that returns nothing is also allowed, and the exit code is then 0:

void main() {
    println("Hello again!")
}

Hello again!

#Building an executable

cromo run compiles the program into a temporary folder, runs it and deletes it. To keep the executable, use cromo build:

cromo build hello.cro          # writes hello.exe on Windows, hello on Linux
./hello

By default cromo builds a debug executable: it is optimized, but it checks every integer operation for overflow, and it contains the information that a debugger needs. With --release integers wrap around on overflow, as in C, and the executable is smaller:

cromo build --release hello.cro

The executable runs on any machine with the same system, without installing anything. cromo can also write an executable for the other system:

cromo build --target linux hello.cro     # on Windows: an executable for Linux
cromo build --target windows hello.cro   # on Linux: hello.exe for Windows

#A project

A project is a folder with a file main.cro. Without a file name, cromo build, cromo run and cromo test use the main.cro of the current folder, and the executable is named after the folder:

mkdir greeter
cd greeter
# write main.cro
cromo run

The other files of the folder are modules, which main.cro imports by name: chapter 11 explains them.

#Formatting

Cromo code has one style, and cromo fmt writes it: four spaces of indentation, the opening brace on the same line, one space around operators. There are no options to discuss:

cromo fmt                 # every .cro file of this folder and its subfolders
cromo fmt hello.cro       # one file
cromo fmt --check         # only lists the files that are not formatted

#Visual Studio Code

The Cromo extension, which the installation adds to Visual Studio Code, colors the code and uses cromo lsp, the language server of Cromo, to show:

• the errors while you write, without compiling by hand;
• the type and the declaration of a name, when the mouse is over it;
• the definition of a name, with F12;
• the members of a value, after a dot;
• the formatting of the file, when it is saved.

Any editor that speaks the Language Server Protocol can use cromo lsp in the same way.

#Summary

• cromo run file.cro compiles and runs a program; cromo build writes the executable.
• A program starts from main, which returns its exit code.
• The type comes before the name; ret returns; statements end at the end of the line.
• cromo fmt formats the code, and the extension for Visual Studio Code shows the errors while you write.

In the next chapter you will write a complete program, before learning the details.