The L Programming Language
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Hello World in L

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The L Programming Language

The L Programming Language is an experimental, minimalist, multi-paradigm programming language. It is designed around the radical philosophy that programs should be intelligible and easy to reason about. Therefore, the core syntax is concise but extensible and the language semantics can be extended through a safe macro system.

Design Goals

The L Programming Language is designed to be intuitive and easily comprehensible after learning the foundational building blocks of the syntax. The syntax is distinctive in its lack of reserved words and its structural simplicity.

The language's built-in concurrency semantics combined with a powerful runtime make it easy to write distributed concurrent programs.

Notable Features

  • Pattern Matching: One of the first surprising features of L is that it does not have an assignment operator. Instead, it uses a pattern matching "bind" operator to structurally map values onto their corresponding variables.

    [x, y..., z] :: [16, 25, 36, 49, 64]    # x == 16, y == [25, 36, 49], and z == 64
  • Gradual Typing: Variables are not required to explicitly state the data type of the value they contain. The runtime is able to infer most of the necessary type information to run a program, but when a programmer wishes to add additional constraints to an implementation, they can add explicit types for compile-time checking.

  • First-Class, Anonymous Functions: All functions in L are first-class values. A function may receive another function as an argument and return a function as a result. Functions in L are not named, but they may be assigned to variables just like any other value.

  • Algebraic Data Types: There are two main user-definable data types in L. Unions are collections of two or more named variants. The Boolean data type is an example of a union having variants for True and False. Records are values that are collections of named fields. Cartesian points, for example, could be represented as a record, having values for their x and y components.

There are far more features than can be highlighted here, so the best place to learn more is the Introduction to the L Programming Language.

Installing L

Clone the repository and from within the newly created project directory, run the following commands:

npm install
npm run metal

The npm run metal command starts the interactive shell.

Using the Interactive Shell

L comes with an interactive shell. After building the project, run npm run metal to start the shell. You'll see an L prompt like this:

The L Programming Language, Meta-L v0.2.02
>>

You can type any L program at the >> prompt and it will be evaluated and the result will be printed on the next line.

In the documentation, we include transcripts of a programmer interacting with the shell. Shell transcripts are formatted in monospaced text, and anything the programmer would type is in bold.

Here's a simple example of an L program:

>> ['Hello', 'world'](join: ', ') + '!'
'Hello, world!'

You've made it this far, so consider reading the Intruduction to the L Programming Language next!