Fantom

Fantom is a JVM-based object-oriented and functional language first appearing in 2005.

Hello World

#!/usr/bin/env fan
// BEGIN_FRAGLET
using [java] java.lang

class Fraglet
{
  Void main()
  {
    System.out.println("Hello World!")
  }
}
// END_FRAGLET

Coding Guide

Language Version

Fantom 1.0.82, JVM-based

Execution Model

• The container runs your fraglet as a Fantom script: fan hello-world.fan [args...]
• Your fraglet is the entire runnable class: it replaces the whole class definition between the injection markers
• Use class Fraglet with Void main() — the runtime discovers and invokes the main method
• Stdin is available via Env.cur().in; arguments via Env.cur().args

Fragment Authoring

Write a complete class with a main() method. The fraglet is the full class. That gives you:

• Arguments: Env.cur().args returns Str[] (command-line args)
• Stdin: Env.cur().in — read lines with in.readAllStr() or line-by-line
• Output: echo("message") or Env.cur().out().printLine("message")
• Full freedom to define methods, fields, and nested types in the class

The class must be named Fraglet (matches the template).

Stdin and Args (for AI / scripts)

• Read stdin: Env.cur().in.readAllStr() or read line-by-line and process
• Use args: Env.cur().args.join(" ") — they are passed through from the fraglet invocation

Key Characteristics

• JVM-based, statically typed
• Case-sensitive; semicolons optional
• Classes and mixins; nullable types with ?
• Built-in prelude: echo, Int, Str, List, etc.

Common Patterns

• Print: echo("message") or Env.cur().out().printLine("message")
• String interpolation: "Total: $count" or "Total: ${expression}"
• Args: Env.cur().args.join(" ")
• Stdin: Env.cur().in.readAllStr() or iterate lines
• Lists: list.each |Int n| { sum += n * n }, iteration and accumulation

Examples

Each example below is a full class you can use as the fraglet as-is.

class Fraglet {
  Void main() {
    echo("Hello, World!")
  }
}

class Fraglet {
  Void main() {
    name := "Alice"
    echo("Hello, $name!")
  }
}

class Fraglet {
  Void main() {
    numbers := [1, 2, 3, 4, 5]
    sum := 0
    numbers.each |Int n| { sum += n * n }
    echo("Sum of squares: $sum")
  }
}

class Fraglet {
  Void main() {
    a := 5
    b := 3
    echo("5 * 3 = ${a * b}")
  }
}

class Fraglet {
  Void main() {
    args := Env.cur().args
    echo("Args: " + args.join(" "))
  }
}

class Fraglet {
  Void main() {
    in := Env.cur().in
    in.eachLine |line| { echo(line.upper) }
  }
}

Notes

• Use class Fraglet and Void main() for the entry point
• Env.cur().args and Env.cur().in are available; no extra setup
• echo() is from the prelude; for more control use Env.cur().out()
• Fantom runs on the JVM; Java interop is available via using [java] ...

Fraglet Scripts

Echo Args

#!/usr/bin/env -S fragletc --vein=fantom
class Fraglet {
  Void main() {
    args := Env.cur().args
    echo("Args: " + args.join(" "))
  }
}

Fantom Fortune

#!/usr/bin/env -S fragletc --vein=fantom
class Fraglet {
  Void main() {
    echo("Fantom: Where the JVM gets a makeover and still runs your grandma's Java.")
  }
}

Stdin Upper

#!/usr/bin/env -S fragletc --vein=fantom
class Fraglet {
  Void main() {
    in := Env.cur().in
    in.eachLine |line| { echo(line.upper) }
  }
}

Test

#!/usr/bin/env -S fragletc --vein=fantom
using [java] java.lang

class Fraglet
{
  Void main()
  {
    System.out.println("Hello World!")
  }
}

Connections

Container Info