cst-tokens grammar snippet

index.js

import { prod, tok, sym, Grammar } from '@/helpers';

new Grammar({
  productions: {
  
    // This version of ImportSpecifier uses helpers to be concise:
    *ImportSpecifier() {
      yield eat(prod`Identifier:imported`);
      yield eatMatch(tok`Keyword:as`, prod`Identifier:local`);
    },

    // The helpers were being used to build up instructions/actions
    // Here is what the same production looks like when the actions are written explicitly:
    *ImportSpecifier() {
      yield {
        type: sym.eat,
        value: {
          type: sym.production,
          value: { type: 'Identifier', property: 'imported' },
        },
      };

      yield {
        type: sym.eatMatch,
        value: {
          // passing multiple arguments to the eatMatch helper was actually creating an All production
          type: sym.production,
          value: {
            type: sym.All,
            // this production does not map to a real AST node
            property: undefined,
            props: {
              matchables: [
                {
                  type: sym.terminal,
                  value: { type: 'Keyword', value: 'as' },
                },
                {
                  type: sym.production,
                  value: { type: 'Identifier', property: 'local' },
                },
              ],
            },
          },
        },
      };
    },
    *Identifier() {
      yield eat(tok`Identifier`);
    },
    *[sym.All]({ matchables }) {
      for (const matchable of matchables) {
        yield eat(matchable);
      }
    },
  },
});