First program

Create an empty directory and save the following file as hello.wl:

hello.wl

func main() -> Int {
    print("hello, White");
    return 0;
}

Build it from that directory:

wlc hello.wl

On Windows, the output is hello.exe:

.\hello.exe

On Linux and macOS, the output has no suffix:

./hello

The program prints:

hello, White

What the file contains

main is the entry point of an executable. It returns an Int; that value becomes the process exit status. Returning zero conventionally means success.

func main() -> Int {

print writes its arguments followed by a newline. It belongs to White's prelude, so this program does not need an import for it.

print("hello, White");

Statements end with a semicolon. Blocks use braces, and the closing brace does not take another semicolon.

Add a function

The next version keeps main small and constructs the message in a separate function:

hello.wl

func greeting(name: String) -> String {
    return "hello, " + name;
}

func main() -> Int {
    let message = greeting("White");
    print(message);
    return 0;
}

Parameters use : between the name and type. The arrow following the parameter list is reserved for the return type. A declaration with an initializer may omit its type when the compiler can infer it, as message does here. Writing let message: Auto = ... is also valid when an explicit inferred type is useful.

Compile the file again with the same command. wlc replaces the previous output after the build succeeds.

Choose another output name

Use -o when the executable should not be named after the source file:

wlc hello.wl -o greeting

On Windows, include the intended suffix:

wlc hello.wl -o greeting.exe

wlc reports compiler errors with the source file, line, column, and the part of the line which caused the problem. A failed frontend check does not proceed to native code generation or replace a successful output from an earlier build.