Ballerina

The Ballerina programming language is pirouetting into the tech world with a grand jeté of features. Designed to handle the choreography of network services, Ballerina twirls effortlessly through data and integrations, making your code en pointe. It's a pas de deux with cloud-native infrastructure, ensuring your deployments are as graceful as a prima ballerina's performance. So, if you want your applications to dance seamlessly across platforms, Ballerina will have your projects en avant. Break a leg! 🩰💃

Hello World

import ballerina/io;

// BEGIN_FRAGLET
public function main() {
    io:println("Hello World!");
}
// END_FRAGLET

Coding Guide

Language Version

Ballerina (latest via SDKMAN)

Execution Model

• Compiled language that builds to JAR files
• Code runs inside the main() function
• Requires ballerina build then ballerina run
• Execution handled by wrapper script

Key Characteristics

• Statically typed
• Case-sensitive
• Java-like syntax with functional features
• Built-in support for network services, data structures, and concurrency

Fragment Authoring

Write valid Ballerina code. Your fragment becomes the module body. This means:

• You must include public function main() { ... } in your fragment
• You CAN define functions, types, and other module-level constructs
• Functions are defined at module level, then called from main()

This approach enables teaching the full range of Ballerina features.

Available Modules

• ballerina/io - Input/output operations (already imported)
• Standard library modules available via import ballerina/<module>;

Command-line arguments

Arguments passed to your script are available as rest parameters in main. Use public function main(string... args) and iterate with foreach:

public function main(string... args) {
    foreach string arg in args {
        io:println(arg);
    }
}

Stdin

Use io:readln() from the ballerina/io module to read a line from stdin. Some versions require a prompt string (use io:readln("") for none). It returns string? (nil at EOF). For line-by-line processing, loop until readln() returns nil:

public function main() {
    string? line = io:readln("");
    if line is string {
        io:println(line);
    }
}

For uppercase output, use string:toUpperAscii() from the ballerina/lang.string module where available.

Common Patterns

• Print: io:println("message");
• Variables: int x = 5; or var x = 5;
• Strings: string msg = "Hello";
• Arrays: int[] numbers = [1, 2, 3];
• Functions: Define at module level, call from main()
• String interpolation: io:println("Value: " + value.toString());

Examples

// Simple output
public function main() {
    io:println("Hello, World!");
}

// Variables and calculations
public function main() {
    int a = 5;
    int b = 10;
    io:println("Sum: " + (a + b).toString());
}

// Function definition (at module level)
function greet(string name) returns string {
    return "Hello, " + name + "!";
}

public function main() {
    io:println(greet("Alice"));
}

// Arrays and loops
public function main() {
    int[] numbers = [1, 2, 3, 4, 5];
    int sum = 0;
    foreach int n in numbers {
        sum += n;
    }
    io:println("Array sum: " + sum.toString());
}

// Multiple helper functions
function add(int a, int b) returns int {
    return a + b;
}

function multiply(int a, int b) returns int {
    return a * b;
}

public function main() {
    io:println("5 + 3 = " + add(5, 3).toString());
    io:println("5 * 3 = " + multiply(5, 3).toString());
}

Caveats

• Fragment must include public function main() or public function main(string... args)
• Code must be valid Ballerina syntax
• Statements end with semicolons
• Type annotations are optional but recommended
• String concatenation uses + operator
• Numbers must be converted to strings for output: value.toString()
• io:readln() returns string?; check for nil when reading multiple lines or at EOF

Fraglet Scripts

Echo Args

#!/usr/bin/env -S fragletc --vein=ballerina
public function main(string... args) {
    foreach string arg in args {
        io:println(arg);
    }
}

Stdin Upper

#!/usr/bin/env -S fragletc --vein=ballerina
public function main() {
    string? line = io:readln("");
    if line is string {
        io:println(line);
    }
}

Test

#!/usr/bin/env -S fragletc --vein=ballerina
public function main() {
    io:println("Hello World!");
}

Connections

Container Info