Function parseProgram

src/prolog/parser.js:8–225

(src)

}

export function parseProgram(src) {
  const tokens = tokenize(stripComments(src));
  let index = 0;

  function peek() { return tokens[index]; }
  function eat(type, value) {
    const tok = tokens[index];
    if (!tok || tok.type !== type || (value && tok.value !== value)) {
      throw new Error(`Parse error near token ${JSON.stringify(tok)}; expected ${type} ${value ?? ''}`);
    }
    index++;
    return tok;
  }

  function parseClause() {
    const head = parseExpression();
    let bodyAst = null;

    if (peek() && peek().type === 'sym' && peek().value === ':-') {
      eat('sym', ':-');
      bodyAst = parseGoalOr();
    }

    eat('sym', '.');
    const bodies = bodyAst ? expandGoals(bodyAst) : [[]];
    return bodies.map((body) => ({ head, body }));
  }

  function parseGoalOr() {
    let left = parseGoalAnd();
    while (peek() && peek().type === 'sym' && peek().value === ';') {
      eat('sym', ';');
      const right = parseGoalAnd();
      left = { type: 'or', left, right };
    }
    return left;
  }

  function parseGoalAnd() {
    let left = parseGoalUnary();
    while (peek() && peek().type === 'sym' && peek().value === ',') {
      eat('sym', ',');
      const right = parseGoalUnary();
      left = { type: 'and', left, right };
    }
    return left;
  }

  function parseGoalUnary() {
    const tok = peek();
    if (tok && tok.type === 'sym' && tok.value === '\\+') {
      eat('sym', '\\+');
      const goal = parseGoalUnary();
      return { type: 'not', goal };
    }
    if (tok && tok.type === 'sym' && tok.value === '(') {
      eat('sym', '(');
      const inner = parseGoalOr();