parser.js

import skipSpace from "./skipSpace.js";

function parseApply(expr, program) {
  program = skipSpace(program);
  if (program[0] != "(") {
    return { expr: expr, rest: program };
  }
  program = skipSpace(program.slice(1));
  expr = { type: "apply", operator: expr, args: [] };

  while (program[0] != ")") {
    let arg = parseExpression(program);
    expr.args.push(arg.expr);
    program = skipSpace(arg.rest);

    if (program[0] == ",") {
      program = skipSpace(program.slice(1));
    } else if (program[0] != ")") {
      throw new SyntaxError("Ожидается ',' или ')'");
    }
  }

  return parseApply(expr, program.slice(1));
}

function parseExpression(program) {
  program = skipSpace(program);
  let match, expr;

  if ((match = /^["']([^"']*)["']/.exec(program))) {
    expr = { type: "value", value: match[1] };
  } else if ((match = /^\d+\b/.exec(program))) {
    expr = { type: "value", value: Number(match[0]) };
  } else if ((match = /^[^\s(),#"]+/.exec(program))) {
    expr = { type: "word", name: match[0] };
  } else {
    throw new SyntaxError("Неожиданный синтаксис: " + program);
  }

  return parseApply(expr, program.slice(match[0].length));
}

function parse(program) {
  let { expr, rest } = parseExpression(program);
  if (skipSpace(rest).length > 0) {
    throw new Error("Неожиданный текст после программы");
  }
  return expr;
}

export { parse, parseExpression, parseApply };