function grammar()

in cli/src/generate/dsl.js [218:365]
120 lines of code
30 McCabe index (conditional complexity)

function grammar(baseGrammar, options) {
  if (!options) {
    options = baseGrammar;
    baseGrammar = {
      name: null,
      rules: {},
      extras: [normalize(/\s/)],
      conflicts: [],
      externals: [],
      inline: [],
      supertypes: []
    };
  }

  let externals = baseGrammar.externals;
  if (options.externals) {
    if (typeof options.externals !== "function") {
      throw new Error("Grammar's 'externals' property must be a function.");
    }

    const externalsRuleBuilder = RuleBuilder(null)
    const externalRules = options.externals.call(externalsRuleBuilder, externalsRuleBuilder, baseGrammar.externals);

    if (!Array.isArray(externalRules)) {
      throw new Error("Grammar's 'externals' property must return an array of rules.");
    }

    externals = externalRules.map(normalize);
  }

  const ruleMap = {};
  for (const key in options.rules) {
    ruleMap[key] = true;
  }
  for (const key in baseGrammar.rules) {
    ruleMap[key] = true;
  }
  for (const external of externals) {
    if (typeof external.name === 'string') {
      ruleMap[external.name] = true;
    }
  }

  const ruleBuilder = RuleBuilder(ruleMap);

  const name = options.name;
  if (typeof name !== "string") {
    throw new Error("Grammar's 'name' property must be a string.");
  }

  if (!/^[a-zA-Z_]\w*$/.test(name)) {
    throw new Error("Grammar's 'name' property must not start with a digit and cannot contain non-word characters.");
  }

  let rules = Object.assign({}, baseGrammar.rules);
  if (options.rules) {
    if (typeof options.rules !== "object") {
      throw new Error("Grammar's 'rules' property must be an object.");
    }

    for (const ruleName in options.rules) {
      const ruleFn = options.rules[ruleName];
      if (typeof ruleFn !== "function") {
        throw new Error("Grammar rules must all be functions. '" + ruleName + "' rule is not.");
      }
      rules[ruleName] = normalize(ruleFn.call(ruleBuilder, ruleBuilder, baseGrammar.rules[ruleName]));
    }
  }

  let extras = baseGrammar.extras.slice();
  if (options.extras) {
    if (typeof options.extras !== "function") {
      throw new Error("Grammar's 'extras' property must be a function.");
    }

    extras = options.extras
      .call(ruleBuilder, ruleBuilder, baseGrammar.extras)
      .map(normalize);
  }

  let word = baseGrammar.word;
  if (options.word) {
    word = options.word.call(ruleBuilder, ruleBuilder).name;
    if (typeof word != 'string') {
      throw new Error("Grammar's 'word' property must be a named rule.");
    }
  }

  let conflicts = baseGrammar.conflicts;
  if (options.conflicts) {
    if (typeof options.conflicts !== "function") {
      throw new Error("Grammar's 'conflicts' property must be a function.");
    }

    const baseConflictRules = baseGrammar.conflicts.map(conflict => conflict.map(sym));
    const conflictRules = options.conflicts.call(ruleBuilder, ruleBuilder, baseConflictRules);

    if (!Array.isArray(conflictRules)) {
      throw new Error("Grammar's conflicts must be an array of arrays of rules.");
    }

    conflicts = conflictRules.map(conflictSet => {
      if (!Array.isArray(conflictSet)) {
        throw new Error("Grammar's conflicts must be an array of arrays of rules.");
      }

      return conflictSet.map(symbol => normalize(symbol).name);
    });
  }

  let inline = baseGrammar.inline;
  if (options.inline) {
    if (typeof options.inline !== "function") {
      throw new Error("Grammar's 'inline' property must be a function.");
    }

    const baseInlineRules = baseGrammar.inline.map(sym);
    const inlineRules = options.inline.call(ruleBuilder, ruleBuilder, baseInlineRules);

    if (!Array.isArray(inlineRules)) {
      throw new Error("Grammar's inline must be an array of rules.");
    }

    inline = inlineRules.map(symbol => symbol.name);
  }

  let supertypes = baseGrammar.supertypes;
  if (options.supertypes) {
    if (typeof options.supertypes !== "function") {
      throw new Error("Grammar's 'supertypes' property must be a function.");
    }

    const baseSupertypeRules = baseGrammar.supertypes.map(sym);
    const supertypeRules = options.supertypes.call(ruleBuilder, ruleBuilder, baseSupertypeRules);

    if (!Array.isArray(supertypeRules)) {
      throw new Error("Grammar's supertypes must be an array of rules.");
    }

    supertypes = supertypeRules.map(symbol => symbol.name);
  }

  if (Object.keys(rules).length == 0) {
    throw new Error("Grammar must have at least one rule.");
  }

  return {name, word, rules, extras, conflicts, externals, inline, supertypes};
}