Wasm::Emitter

# Create an instance of the emitter, which can emit a module.
my $emitter = Wasm::Emitter.new;

# Import fd_write
my $fd-write-type = $emitter.function-type:
        functype(resulttype(i32(), i32(), i32(), i32()), resulttype(i32()));
my $fd-write-index = $emitter.import-function("wasi_unstable", "fd_write", $fd-write-type);

# Declare and export a memory.
$emitter.export-memory("memory", $emitter.memory(limitstype(1)));

# Write 'hello world\n' to memory at an offset of 8 bytes
my $offset-expression = Wasm::Emitter::Expression.new;
$offset-expression.i32-const(8);
$emitter.active-data("hello world\n".encode('utf-8'), $offset-expression);

# Generate code to call fd_write.
my $code = Wasm::Emitter::Expression.new;
given $code {
    # (i32.store (i32.const 0) (i32.const 8))
    .i32-const(0);
    .i32-const(8);
    .i32-store;
    # (i32.store (i32.const 4) (i32.const 12))
    .i32-const(4);
    .i32-const(12);
    .i32-store;
    # (call $fd_write
    #   (i32.const 1) ;; file_descriptor - 1 for stdout
    #   (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
    #   (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
    #   (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
    # )
    .i32-const(1);
    .i32-const(0);
    .i32-const(1);
    .i32-const(20);
    .call($fd-write-index);
    # Drop return value
    .drop;
}

# Declare and export the start function.
my $start-type = $emitter.function-type: functype(resulttype(), resulttype());
my $start-func-index = $emitter.function: Wasm::Emitter::Function.new:
        :type-index($start-type), :expression($code);
$emitter.export-function('_start', $start-func-index);

# Assemble and write to a file, which can be run by, for example, wasmtime.
my $buf = $emitter.assemble();
spurt 'hello.wasm', $buf;