kerolox/tree-sitter-kerolox/grammar.js

/**
 * @file Kerolox grammar for tree-sitter
 * @license AGPL-3.0-or-later
 * 
 * Copyright (C) 2025-2026 Marceline Cramer
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * This file is part of Kerolox.
 *
 * Kerolox is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version.
 *
 * Kerolox is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for
 * more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with Kerolox. If not, see <https://www.gnu.org/licenses/>.
 */

/// <reference types="tree-sitter-cli/dsl" />
// @ts-check

/// A comma-separated list.
const list = el => optional(seq(el, repeat(seq(",", el)), optional(",")))

/// A paren-surrounded, comma-separated list.
const parenList = el => seq("(", list(el), ")");

/// A list that requires a comma for unit length.
const listComma = el => optional(choice(seq(el, ","), seq(el, repeat1(seq(",", el)), optional(","))))

/// A paren-surrounded list that requires a comma for unit length.
const parenListComma = el => seq("(", listComma(el), ")")

/// Shorthand to write a binary expression with left precedence of the given priority.
const expr_prec = (expr, precedence, op) => prec.left(precedence,
  seq(field("lhs", expr), field("op", op), field("rhs", expr)))

export default grammar({
  name: "kerolox",

  extras: $ => [$._whitespace, $.comment],

  rules: {
    file: $ => repeat(choice(
      // explicitly parse newlines and comments separately
      // this helps determine which comments are doc comments
      $.newline, $.comment,
      // the actual items
      $.type_alias, $.import, $.relation, $.rule, $.assumption
    )),

    comment: $ => seq(";", $.commentInner),
    commentInner: _ => /[^\n]*\n/,
    newline: _ => /[\n\r]/,
    _whitespace: _ => /[ \n\r\t]/,
    docs: _ => /(?:;.*\n)*/,

    variable: _ => /[a-z][a-zA-Z0-9_]*/,
    symbol: _ => /[A-Z][a-zA-Z0-9]*/,
    _ident: $ => choice($.variable, $.symbol),

    integer: _ => choice("0", /-?[1-9][0-9]*/),

    type_alias: $ => seq(
      "type",
      field("name", $.symbol),
      "=",
      field("type", $.type),
    ),

    type: $ => choice(
      field("named", $.name),
      parenListComma(field("tuple", $.type)),
    ),

    import: $ => seq(
      "import",
      field("path", $.symbol),
      repeat(seq(".", field("path", $.symbol))),
      ".",
      choice(
        field("item", $.symbol),
        parenList(field("item", $.symbol))
      ),
    ),

    relation: $ => seq(
      "define",
      field("input", optional("input")),
      field("output", optional("output")),
      field("decision", optional("decision")),
      field("name", $.symbol),
      field("type", $.type),
    ),

    rule: $ => seq(
      optional(field("negate", "-")),
      field("relation", $.name),
      field("head", $.expr),
      choice(".", seq(":-", field("body", $.rule_body))),
    ),

    assumption: $ => seq(
      optional(seq("soft", "(", field("soft", $.integer), ")")),
      ":-",
      field("body", $.rule_body),
    ),

    name: $ => prec.left(seq(repeat(seq(field("path", $.symbol), ".")), field("path", $.symbol))),

    rule_body: $ => seq(list(field("clause", $.expr)), "."),

    expr: $ => choice(
      // variables
      field("hole", "_"),
      field("variable", $.variable),

      // composites
      field("apply", $.apply),
      field("tuple", $.tuple),
      field("aggregate", $.aggregate),

      // value literals
      field("true", "True"),
      field("false", "False"),
      field("symbol", $.name),
      field("integer", $.integer),

      // operations
      field("unary", $.unary_expr),
      field("binary", $.binary_expr),

      // nested
      seq('(', field("parens", $.expr), ')'),
    ),

    apply: $ => prec.right(2, seq(field("head", $.name), field("body", $.expr))),

    tuple: $ => parenListComma(field("el", $.expr)),

    aggregate: $ => seq(
      field("op", $.aggregate_op),
      optional(seq(list(field("witness", $.variable)), ":")),
      choice(
        field("apply", $.apply),
        seq("{", list(field("clause", $.expr) ), "}"),
      ),
    ),

    aggregate_op: $ => /@[a-z]+/,

    unary_expr: $ => prec.left(5, seq(
      field("op", $.unary_op),
      field("term", $.expr)
    )),

    unary_op: _ => choice("!", "-"),

    binary_expr: $ => choice(
      expr_prec($.expr, 4, choice("*", "/")),
      expr_prec($.expr, 3, choice("+", "-")),
      expr_prec($.expr, 2, choice("..", "++")),
      expr_prec($.expr, 1, choice("=", "!=", ">=", "<=", "<", ">")),
      expr_prec($.expr, 0, choice("&&", "||")),
    ),
  }
});