Basic Program Structure

For now, Par lacks a proper module system. Each program is contained in one file, with built-in names imported automatically.

These built-in names are scoped in modules — for example, Int.Add is a function called Add in the Int module — but there is no way to define custom modules. All we can do is define types and values, and then run them, interactively!

Before we start defining our own types and values, the built-in definitions already give us something to play with.

Let’s open the playground!

$ par-lang playground

Press Compile, then hit the Run button:

All the built-in names are there. Let’s run Int.Add:

An automatic UI shows up, telling us to input two numbers. After confirming both inputs, we get a result:

The playground features an automatic UI. Nobody made a specific interaface for this Int.Add function. Instead, the UI that shows up is based purely on its type — here, a function from two integers to an integer result.

Go ahead, and play with any built-in definition! Then, when you turn the page, we’re going to talk about creating our own.