Hello World

A humble greeting from SMLL

Well you are here! That means you now have the smll compiler working on your system and now we are going to write and compile a simple "hello world" program to demonstrate how the language mostly looks like.

hello.smll

using System::Io

fun main(): Unit => println("Hello, world")

Here we are doing the following:

using System::Io

This imports code definitions from the Io module in the System namespace. More on namespaces and modulesI

fun main(): Unit => println("Hello, world")

This defines a function called main which receives zero arguments and returns Unit. Unit is a type similar to void in JAVA, more on type on the coming sections. The arrow operator is used to separate the function header from the body expression. In smll functions only have one expression as the body. In this case we simply call the function println with the argument "Hello, world" passed as input to the function. The println function is imported from the Io module, remember? The println function also returns unit so the return value gets promoted to the return of main.

Compile it

To compile run the following command.

Before compiling smll expects a build directory to be present in the root directory of your project. If you have created a build folder run the following command to do so.

$ mkdir build

This is going to be replaced by a compiler command argument for creating a project structure.

./target/debug/smll hello.sml

You should then get the following output

Writing ir to file: `Hello.java`
process exited with status: exit status: 0 

The exit status is from the java compiler process which just compiled the output file "Hello.java"

Run it!

To run the compiled program use the java compiler like so.

java --enable-preview --source 21 Hello.java  

or pass an extra command line argument like --run to automatically invoke the java compiler for you and run your code.

./target/debug/smll --run hello.sml