bason-script

BASON Script

A lightweight Javascript interpreter for a JSON-based scripting language.
BASON is an acronym for: Basic Abstract Syntax Object Notation** **

Syntax

• A Program in BASON Script is contstructed as a valid JSON object and contains a script
• A Script is an array of expressions to be evaluated.
• An Expression is a literal (string or number), or an object who's key is a keyword (Command, Function, or Variable) and value is its input parameter(s).
• Parameters are also an array of expressions. If there's only one parameter, there's no need for the containing array.

Examples

Hello World:

[{ PRINT: 'Hello World!' }]

Each program is an array of expressions, and therefore wrapped in square brackets. This script only has one expression, an object whos key is the name of the command, in this case PRINT, and we supply it with a string literal which results in the text "Hello World!" printing to the console.

Using Variables:

[
  { LET: ['myvar', 'World!'] },
  { PRINT: { ADD: [ "Hello ", {myvar: null} ] } }
]

In this example we define a variable with the LET command. LET takes two parameters, the name of the variable and its value. We then use the ADD function to join the text "Hello " with the value of myvar to get "Hello World!" and print the result to the console with PRINT. In BASON Script, Variables are referenced as objects with a null value.

Using Loops:

[
  { LET: ['i', 0] },
  { REPEAT: 10, script: [
    { SET: ['i', { ADD: [ {i: null}, 1 ] }] },
    { PRINT: {i: null} },
  ] }
]

This program prints the numbers 1 to 10 to the console using the REPEAT command. Any command which executes a script such as loops takes a special object property called "script" who's value is a script array.

Functions:

[
  { FUNCTION: ['GREET', 'name'], script: [
    { PRINT: { ADD: ['Hello ', { name: null }] } }
  ] },
  { GREET: 'Dan' }
]

Here we define a new function called GREET with an input parameter called name. Once it has been defined, we can use it the same as any other command. Presently, functions are not hoisted, so you must declare a function before it is used in a script. Functions are locally scoped, so any variables or functions declared in them will not be accessible outside and will shadow anything of the same name in the outer scope.

Usage

But why?

BASON Script's syntax is obviously painful to write, so why would you want to use it? Well it has a couple of interesting use cases.

• A safe method of transmitting and executing arbitrary server-side code in a sand-boxed environment.
• The syntax is essentially an Abstract Syntax Tree, making it an ideal target data format for creating new languages and parsers

Running the Demo

• npm run demo will run the example program located in demo/index.js