count-identifiers.js es6 version

count-identifiers.js

//depends on shift-parser, shift-reducer, and shift MonoidalReducer
import parse from "shift-parser";
import reduce, {
  MonoidalReducer
}
from "shift-reducer";

//IdentifierCounter inherits from MonoidalReducer
class IdentifierCounter extends MonoidalReducer {

  //reduce over a shift ast counting the Identifiers
  static count(program) {
    return reduce(new this, program);
  }

  //must return a Monoid
  constructor() {
    super(class Sum {
      //by default reduce a 0 for any node
      static empty() {
          return 0;
        }
        //override concat to sum nodes
      concat(a) {
        return this + a;
      }
    });
  }

  //only need to override MonoidalReducer for IdentifierExpressions to count number of Identifiers
  reduceIdentifierExpression(node, identifier) {
    return 1; //will be summed 
  }
}

//test code 
let program = `function f() { hello(world); }`;
console.dir(IdentifierCounter.count(parse(program)));