FunctionalScript

FunctionalScript is a pure functional programming language and a strict subset of ECMAScript/JavaScript. It's inspired by

• JSON as a subset of JavaScript. JSON is also a subset of FunctionalScript.
• asm.JS/WebAssembly, as a subset of JavaScript.
• TypeScript, as a superset of JavaScript.

Create a new FunctionalScript repository on GitHub here.

Try FunctionalScript here.

1. Design Principles

In FunctionalScript:

• Any module is a valid JavaScript module. No additional build steps are required.
• Code should not have side-effects. Any JavaScript statement, expression, or function which has a side effect is not allowed in FunctionalScript. There are no exceptions to this rule, such as unsafe code which can be found in Rust, C#, and other languages.
• A module can't depend on non FunctionalScript module.
• It also has no standard library, only a safe subset of standard JavaScript API can be used without referencing other modules.

2. Outlines

2.1. Module Ecosystem

FunctionalScript uses CommonJS conventions as a module ecosystem. For example,

const thirdPartyModule = require('third-party-package/module')

const result = thirdPartyModule.someFunction('hello')

2.2. Packages

FunctionalScript uses a package.json file to define a package. This file is compatible with Node.js package.json. The prefered way to refence dependencies is to use a GitHub URL. These dependencies in a package.json file could look like this,

{
   // ...
   "dependencies": {
      "third-party-package": "github:exampleorg/thirdpartypackage"
   }
   // ...
}

Note: this repository is also a FunctionalScript package, and it can be used as a library. To install this package, use

npm install -S github:functionalscript/functionalscript

2.3. Module Structure

A module is a file with the .js extention. It contains three parts: references to other modules, definitions, and exports. For example

./first.js

// 1. references
const math = require('math')

// 2. definitions
const myConst = 42
// addition(a)(b) = a + b
const addition = a => b => a + b
const add42 = addition(42)
const _10digitsOfPi = math.calculatePi(10)

// 3. exports
module.exports = {
   addition,
   add42,
   _10digitsOfPi,
}

./second.js

// 1. references
const first = require('./first.js')

// 2. definitions
const _42plus7 = first.add42(7)

// 3. exports
module.exports = {
   _42plus7,
}

2.4. References To Other Modules

The format of references is const ANYNAME = require('PATH_TO_A_MODULE'). For example,

const math = require('math')
const algebra = require('math/algebra')
const localFile = require('../some-directory/some-file.js')

2.5. Definitions

The format of defintions is const NAME = EXPRESSION, where the EXPRESSION is a subset of JavaScript expressions.

const myConst = 42
const functionDouble = a => a * 2
const structure = { name: "John", surname: "Smith" }
const array = [1, 2, 3]
const nestedStructure = { 
   address: undefined, 
   serialNumber: "123-45-78", 
   sum: 14 + myConst + functionDouble(4),
   moreInfo: { 
      name: "Ivan",
      surname: "Terrible",
   } 
}

See 3. Expressions.

2.6. Exports

The format of exports is module.exports = { A_LIST_OF_EXPORTED_DEFINITIONS }. There should be only one module.exports at the end of a FunctionalScript file. For example,

module.exports = {
   nestedStructure,
   array,
   structure,
}

3. Expressions

Expressions could fall under these categories:

• Literals:
  • Number Literals, e.g. 0, 3.14, 4e8
  • Boolean Literals: true or false
  • A null Literal
  • An undefined Literal
  • String Literals, e.g. "Hello world!"
• Complex Structures
  • Arrays, e.g. [2, 5]
  • Objects, e.g. { a: "Hello", b: "world!" }
  • Arrow functions, e.g. x => x * 2
• Operators
  • Comparison Operators: ===, !==, >, >=, <, <=
  • Arithmetic Operators: +, -, *, /, %, **
  • Bitwise Operators: &, |, ^, ~, <<, >>, >>>
  • Logical Operators: &&, ||, !, ??
  • Conditional Operator, e.g. condition ? val1 : val2
  • Template Literals, e.g. string ${expression}
  • typeof
  • Relations Operators: in, instanceof.
  • Member Operators: ., [].

Note: the . member operator has prohibitted property names, such as constructor and push. To access such properties, it's recommeded to use the Object.getPropertyDescriptor function.

4. Arrow Functions

An arrow function is also known as a lambda function. The format of an arrow function is ARGUMENT_NAME => FUNCTION_BODY. An arrow function must have either a single argument or no arguments at all. For example

x => x * 2
a => a + 4
s => `template literal ${s}`
a => b => a + b // an arrow functions that returns another arrow functions.
() => 'hello' // an arrow function with no arguments

A function body is either an expression or a block statement. A block statement format is { A_LIST_OF_STATEMENTS }. For example

// a function with one argument and a block statement
const f = x => {
   const a = 2 + x
   const r = a + 4
   return r
}