module.exports = grammar({
  name: 'dust',

  rules: {
    source_file: $ => repeat(choice(
      $.comment, 
      $.expression,
      $.yield,
      $.chain
    )),

    expression: $ => choice(
      prec(2, $.value),
      prec(1, $.identifier),
      $.tool,
      seq($.identifier, $.operator, $.expression),
    ),

    value: $ => choice(
      $.integer,
      $.float,
      $.string,
      $.list,
      $.empty,
      $.boolean,
    ),
  
    comment: $ => /(#)(.+?)([\n\r])/,

    yield: $ => "->",

    chain: $ => ";",
    
    identifier: $ => /[a-zA-Z|_|.]+(_[a-zA-Z]+)*/,

    operator: $ => choice(
      '=',
      '-',
      '+',
      '/',
      '|',
      '&'
    ),

    tool: $ => choice(
      "random",
      "random_boolean",
      "random_integer",
      "random_string",
      "random_float"      
    ),

    float: $ => /\d+\.\d*/,
    
    integer: $ => /\d+/,

    string: $ => seq(
      '"',
      repeat(),
      '"'
    ),

    function: $ => /\{(.*?)\}/,

    empty: $ => "()",

    boolean: $ => choice(
      "true",
      "false"
    ),

    list: $ => seq(
      '(',
      repeat1(seq($.expression, optional(','))),
      ')'
    ),
  }
});