The programming language for scalable development

import Core'Number
import Os'File

# The `\` prefix for λ denotes a function.
findAnswer = \(kind string) number {
  # Secret source...

  21
}

main = \(ctx context) none {
  # The `go` function runs a given function in parallel.
  # `x` is a future for the computed value.
  x = go(\() number { findAnswer("humanity") })
  y = findAnswer("dolphins")

  _ = File'Write(ctx, File'StdOut(), Number'String(x() + y))

  none
}

Vision

Pen aims to make large-scale software development efficient where many engineers develop software together for a long time. To realize that, it focuses on software maintainability and portability.

• Maintainability
  • Simplicity: The language is small and easy to learn yet full featured.
  • Testability: Tests are always fast and reliable.
  • Flexibility: Developers can change codes easily without regression.
• Portability
  • Programs written in Pen can be ported to different platforms including WebAssembly.

Features

Minimal language

• Its syntax and type system are small, simple, and easy to learn.
• Yet, the language supports all the modern features.

Concurrent/parallel computation

• The language and its runtime enables thread-safe concurrent/parallel computation.
• For more information, see Concurrency and parallelism.

Reliable testing

• Tests are always deterministic and fast.
• Tests are side-effect free and independent from test environment.

No built-in system library

• There is no built-in system library dependent on platforms.
• Developers choose system packages suitable for their applications.
• System packages encapsulate platform-dependent codes and side effects.
• No other kind of package causes side effects without explicit injection.

Security

• No runtime exception
• Memory safe
• No undefined behavior
• No data race

Even more…

• Static typing
• Immutable values
• Pure functions by default
• Errors as values
• Asynchronous I/O
• Cross compile
• Rust/C Foreign Function Interface (FFI)

License

Pen is dual-licensed under MIT and Apache 2.0.