First Program (Hello World)

Ah, the hello world. The first program that one makes in a new language. The sanity check that all is well. In Asylum, making such a program is relatively straight-forward:

println("Hello World!");

Output:

Hello World!

Understanding The Program

That’s it. Now, let’s understand what this syntax means:

• println is a function that prints what you give it, then goes to the next line. You call a function by putting its parameters between ( and ), with the parameters being comma-separated. You can see here that we are telling it to print Hello World!. We must wrap this value in "s so the compiler knows that it’s a value that we are sending it.

• There is a semicolon ; to signal to the compiler that the statement is over.

Notice that statements outside a function are called top-level statements. These are only allowed to be in one of the files you are compiling, as the compiler wouldn’t know where your program would start otherwise. Normally, we put code inside of functions to be more organized:

fn main()
{
    println("Hello World!");
}

Output:

Hello World!

Understanding The Function Syntax

That’s it. Now, let’s understand what this syntax means:

• When you run an Asylum program, it will run the function called main (or top-level statements in one file if main doesn’t exist).

• We declare a function by using the keyword fn.

• After that, we give it the name of our function, which in this case is main.

• After this, we have an empty pair of parenthesis, (). We will use this later to give functions arguments, but do not worry about this for now.

• We put any code statments we want to run inside the function within {}.

• If this is confusing, don’t worry, we will talk about a lot of this individually later!

A Cool Trick

Asylum also lets you do a shortcut for any function that is only one expression:

fn main() => println("Hello World!");

Output:

Hello World!

The same output is produced. For now, you can think of {} as a group of many code statements, where => will just return one expression.

Warning

`=>` must be used in combination with an expression. A call to `println` is allowed, as function calls are part of an expression. However, items such as blocks, if statements, loops, etc. are not allowed as they are not expressions.

Print Function

While println exists, print also exists too? So what’s the difference? println will put a newline after it prints what you give it, while print will not. For example:

fn main()
{
    println("1");
    println("2");
    print("3");
    print("4");
    println("5")
    print("6")
    println("7");
}

Output:

1
2
345
67

Comments

Comments are not read by the compiler, and are also very important to documenting your code:

// This is a single line comment.
/*
    This is a mult-line comment.
    Anything within the bouncers is not read by the compiler.
*/

Challenges

1. Write a program that says “Hello Asylum User!” in one line of code two different ways.

2. Write a program that prints the first 3 letters of the alphabet together, but you are only allowed to print one letter at a time.

Challenge Solutions

• Solution 1

• Solution 2