grammar.js

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

  word: $ => $.identifier,

  rules: {
    program: $ => seq(repeat1($.edges), repeat1($.imports), $.probability),

    edges: $ =>
      choice(
        seq($.identifier, choice('->', '→'), $.identifier),
        seq($.edges, choice('->', '→'), $.identifier)
      ),

    imports: $ => seq('import', '"', $.url, '"'),

    probability: $ => seq('Pr', '(', $.query, optional($.cond), ')'),
    cond: $ => seq('|', $.query),

    land: $ => choice(',', '∧'),
    lor: $ => choice('+', '∨'),
    lxor: $ => choice('^', '⊕'),
    lnot: $ => choice('!', '¬'),
    leq: $ => '=',

    op: $ => choice($.land, $.lor, $.lxor, $.leq),

    query: $ =>
      choice(
        $.identifier,
        prec.left(1, seq($.lnot, $.query)),
        prec.left(1, seq($.query, $.op, $.query)),
        seq('(', $.query, ')')
      ),

    identifier: $ => /[a-zA-Z_]+/,

    url: $ => /[^\s"]+/,
  },
})