Hello, World!

Write the program

Create a file called hello.mw:

hello.mw

@import("std")

@export fn main(argc: i32, argv: rawptr) -> i32 {
    println("Hello from Marrow !");

    print("Received arg count: ");
    println_i64(cast(i64) argc);

    ret 0;
};

A few things worth noticing already (all covered in depth in the Language reference):

• @import("std") pulls in the standard library’s umbrella module (std/std.mw), which in turn imports io.mw, mem.mw, string.mw, sys.mw, vec.mw and map.mw for you. This is what makes println, print and println_i64 available.
• @export marks main as an externally-visible symbol — required for the C linker to find your entry point.
• argc: i32, argv: rawptr mirrors the C int argc, char** argv signature, since Marrow programs are linked against the C runtime’s _start/main machinery.
• cast(i64) argc explicitly converts the i32 to an i64 before it’s passed to println_i64.
• Every statement ends in ;, including the closing } of the top-level fn declaration.

Compile it

marrow hello.mw

This single command runs the whole pipeline:

1. Parses hello.mw and resolves its @imports.
2. Generates QBE IL into hello.ssa (the default output path — see CLI reference to override it).
3. Invokes qbe hello.ssa -o hello.s to produce native assembly.
4. Since the program is not a library (no @no_main anywhere in the file), invokes your system C compiler to assemble and link hello.s directly into an executable named after the input file with its extension stripped: hello.

On success you’ll see:

Compilation successful! Executable created at: hello

Run it

./hello arg1 arg2

Hello from Marrow !
Received arg count: 3

(argc is 3 because the program’s own name counts as argv[0], per the usual C convention.)

Compiling a library instead of a binary

If your file is decorated with @no_main anywhere (this is how every file in std/ is written), marrow treats it as a library: it stops after producing an object file instead of linking an executable, and tells you how to link it yourself:

Library compiled (no 'main', see '@no_main'): hello.o
Link it into a program with: cc your_program.o hello.o -o your_program

See Modules & decorators for the full explanation of @no_main, @export, @extern and @import.