Name Recipes/Basic/Hello

Synopsis Variations on the ubiquitous Hello World example.

Examples

First version: hello on the command line

We demonstrate hello via an interactive session with the Rascal system. First we get the prompt rascal> that shows that Rascal is ready for our input. Next, we import the library module Rascal:IO since hello world requires printing. Rascal responds with the feedback ok so we know that all went well. Finally, we call println and proudly observe our first Rascal output!

rascal>import IO;
ok
rascal>println("Hello world, this is my first Rascal program");
Hello world, this is my first Rascal program
ok

Second version: hello in a function

A slightly more audacious approach is to wrap the print statement in a function and call it:

rascal>import IO;
ok
rascal>void hello() {
>>>>>>>   println("Hello world, this is my first Rascal program");
>>>>>>>}
void (): void hello();

When you type in a command and continue it on a new line the Rascal systems prompts you with >>>>>>> to indicate that more input is needed. Don't get scared by the void (): void hello(); that you get back when typing in the hello function. The first void () part says the result is a function that returns nothing, and the second part void hello() summarizes its value (or would you prefer a hex dump?). Finally, we call the hello function and enjoy its output.

rascal>hello();
Hello world, this is my first Rascal program
ok

Third version: hello in a module

The summit of hello-engineering can be reached by placing all the above in a separate module:

module demo::basic::Hello

import IO;

void hello() {
   println("Hello world, this is my first Rascal program");
}

Using this Hello module is now simple:

rascal>import demo::basic::Hello;
ok
rascal>hello();
Hello world, this is my first Rascal program
ok

The hello function is by default visible outside the Hello module. We could stress this by adding writing public void hello() { ... }. Restricting visibility to the module itself can be achieved by adding the keyword private to the definition of hello.

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