Hello, WebAssembly

This tutorial walks through writing and running your first woua program step by step.

What you'll build

A program that prints a greeting to the terminal using the io library.

The program

(include io)

(defn main ()
  (printf "hello %s!\n" (string "world")))

What's happening

• (include io) pulls in the I/O library, which itself includes wasi_p1 and string.
• (defn main () ...) declares the entry point — woua exports _start pointing to main.
• (string "world") allocates a String struct on the heap pointing to the static bytes for "world".
• (printf "hello %s!\n" ...) is a compile-time macro that scans the format string and emits the appropriate print calls.

Compile and run

wasmtime --dir . wouac/dist/wouac.wasm hello.woua -o hello.wat
wat2wasm hello.wat -o hello.wasm
wasmtime hello.wasm
# hello world!

Next steps

Continue with Variables and types to learn how to declare locals, work with integers, and define your own struct types.