Though it is possible to continue running any programs by saving it to a file and running it with gluon my_script.glu there is an easier way to go about it when you want to experiment quickly with small programs. By running gluon -i, gluon starts in "interactive" mode, giving you a REPL where you may evaluate expressions and inspect their results. Try evaluating some simple arithmetic expressions to see that it works.

> 1 + 2
3
> 100 * 3 + 4
304
> 3.14 * 10.0
31.400000000000002

Evaluating only a single expression can get quite unwieldy so if we want to break something up into multiple steps we can use let to give a name to an expression.

> let pi_2 = 3.14 * 2.0
6.28
> pi_2 * 3.0
18.84

These are the basic parts of the REPL and if you want to you can try writing hello world again by using the features above.

If you still have the hello_world.glu file around there is another way to run it from inside the REPL by using the special :script (:s) command.

> :s hello_world.glu
Hello World!

There are a few other of these special commands as well and you can find them all with :help (:h).

> :type 1
Int
> :info std.io.println
std.io.println: String -> IO ()
> :kind std.option.Option
Type -> Type

Finally you may quit the REPL using the :quit (:q) command or using <CTRL-D>.