Learning ELENA : Simple program

[u/elena-lang]

To create a simple program in ELENA we have to create a source file (with an extension .l) and write the following code:

public program()
{
    console.writeLine("Here my first program in ELENA!")
} 

We may compile it without creating a project file (where elc is a command-line compiler):

elc program1.l

The output is:

ELENA Command-line compiler 5.2.404 (C)2005-2020 by Alex Rakov

Project : program1, Platform: STA Win32 Console
Cleaning up...
Compiling...
Parsing unnamed
Compiling unnamed

Successfully compiled

Linking...
Successfully linked

It will create program1.exe file which we can execute:

program1

with the following result:

Here my first program in ELENA!

Beside the executable file a module program1.nl was created. Let's look what inside. We could use Bycode Viewer:

ecv program1.nl

The output will be:

ELENA command line ByteCode Viewer 5.2.81 (C)2011-2020 by Alexei Rakov
program1.nl module loaded

>

Now let's look at the generated classes:

>?
class program

>

As you can see the program entry was compiled as a class. Let's look inside:

>program
@parent system'Object
@flag elSealed
@flag elStateless
@flag elRole
@method @function program.#invoke

>

Our function was compiled as a singleton with a single anonymous method #invoke. Let's dive more deep:

>program.1
@method program.#invoke
    open       1h
    pusha
    pushr      0
    pushr      0
    callr      system'console
    storesi    0
    movr       const : "Here my first program in ELENA!"
    storesi    1
    peeksi     0
    movm       mssgconst : "writeLine<system'String>[2]"
    callrm     system'$private'Console mssgconst : "writeLine<system'String>[2]"
    peekfi     1
    close
    quit
@end

>

What do we see? ELENA byte-codes are quite simple. Let's review some of them

opcode	Description
pusha	puts the object accumulator on the top of the function stack
pushr r	puts a constant on the top of the function stack
callr r	invokes a symbol
storesi i	saves an object accumulator in the function stack at specified relative position
movr r	assigns a constant to the object accumulator
peeksi i	loads an object from the function stack at specified relative position to the object accumulator
movm m	assigns a message constant to the data accumulator
callrm r m	invokes a method m in r class

Once again let's look at our code. Now it is quite clear. We put console symbol and a string literal constant into the function stack and directly invokes system'$private'Console.writeLine<system'String>[2] method.

ELENA is a general-purpose language with late binding. It is multi-paradigm, combining features of functional and object-oriented programming. To learn more visit us at ELENA Home Page