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Hello, World

In this chapter, we are going to learn about how to write a basic Hello, World application as well as try our hands on something a little more exiting than that.

At the end of the chapter, you should be more motivated to learn Blade.

Starting the interpreter

If you’ve had any experience at all with programming, then you’ll be familiar with an interactive shell. Incase you don’t know, an interactive shell is an application that when run, prompts for commands, does something based on them (execution) and either prints a result, asks for another command or both in that order.

Blade comes with an interactive shell also knwon as the REPL (Read-Evaluate-Print-Loop) mode. This mode allows you to quickly execute or test out ideas without writing a complete program (Er… depends on what you call a complete program).

To start Blade in the REPL mode, simply type the following command in your terminal.

$ blade

You should be presented with a screen looking like the below:

Blade 0.0.85 (running on BladeVM 0.0.9), REPL/Interactive mode = ON
Clang 13.0.0, (Build time = Feb  8 2022, 02:47:36)
Type ".exit" to quit or ".credits" for more information

You might see a few differences depending on your operating system, the build and version you have installed. However, at a minimum, you should see a welcome message and at lease a version number as well as tips on how to get more help or exit the REPL.

The Blade REPL prompts for the next command with the greater-than (%>) sign or a continuation with the bar (..) sign. You can exit the REPL mode by typing .exit and pressing the ENTER key or simply by pressing the combination Ctrl+D.

The Hello, World program

Following in the footsteps of legends, we are going to start learning Blade by writing a simple Hello, World application. Now, fire up your Blade REPL, type the following and press ENTER.

%> echo 'Hello, World'

You should see the text 'Hello, World' printed immediately after it. Congratulation, you’ve written your first Blade program! The ' surrounding our text is because we are in the REPL and serves as an easy way to identify strings in the REPL output.

Now, let’s try something a little more fun shall we?

Create a file somewhere on your computer and name it hello.b. Now, the following program into the file and save it.

print('Hello, World\n')

Note that print does not add a newline by default

Have you done that? Ok. Now, navigate to the folder/directory containing your file in your preferred terminal (Err… is that Windows? Open the command prompt). Are you there? Now type the following command.

$ blade hello.b

Blade script files can have any name and can end with any extension. But files that can be used as a module or form part of a package MUST end with the .b extension.

Can you see it? Now you are a Blade ninja! You now know two ways to print something to screen and you can use the REPL and a file to create a Blade program. Give yourself a pat on the back and tell yourself weldone. You did good.

For those of you who still can’t see it, pick a sledge hammer, smash your computer and go get something modern.

We’ll learn more about the print thing you saw there later. For now, it’s good enough to know that there are two ways show something on the screen.

  1. Using the echo command
  2. Using the print function

You’ll see how they differ when we explain print better here.

Blade the Calculator

We can take surely have more fun than just printing “Hello, World” to the screen. We can go ahead and do some amazing things now that we know how to print something to screen. How about we take a look at using Blade as a calculator?

When you type simple expressions into the Blade REPL without any command or write an expression without an associated command within a condition, loop or at the end of a function, Blade outputs the result for you. This allows us to do many amazing things in the REPL mode.

Now, let’s try a few more commands in the REPL.

%> 5 + 20
%> 4 * 11
%> 16 - 1 * 4 / 6+3
%> 2 ** 5

In the examples above, we used Blade as a simple arithemetic calculator. Notice that little **? That simply means raise to power and 2 raised to the power of 5 equals 32.

At this point, it’s important to introduce you to three constants in Blade. This constants cannot be changed and have reserved meanings and functions in Blade. They include the boolean true and false as well as nil that denotes the abscence of a value.

If all you ever want to do with Blade is use it as a handy calculator, you are welcomed to stop here. But if you want to do beautiful and amazing things, let’s continue into the next chapter together.

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Copyright © 2021 Ore Richard Muyiwa. Distributed under the MIT license.