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

  rules: {
    source: $ => repeat(choice(
      $.statement,
    )),

    statement: $ => seq($.expression, $.close),

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

    close: $ => ";",

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

    value: $ => choice(
      $.integer,
      $.float,
      $.string,
      $.list,
      $.empty,
      $.boolean,
      $.function,
    ), 

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

    string: $ => /("|'|`)(.*?)("|'|`)/,

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

    empty: $ => '()',

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

    list: $ => seq(
      '(',
      repeat1(seq($.value, optional(','))),
      ')'
    ),

    operator: $ => choice(
      '+',
      '-',
      '=',
    ),
  }
});