old_contents: 'use strict';
  
  const H = require('../interface/result.h').prototype;
  const sym = require('../interface/result-sym.h');
  
  
  H.and = function ($val) {
      if (this[sym.isOk]) {
          this[sym.value] = $val;
      }
  
      return this;
  };
  
new_contents: 'use strict';
  
  const h = require('../interface/result.h');
  const hProto = h.prototype;
  const sym = require('../interface/result-sym.h');
  
  
  H.and = function ($val) {
      return this[sym.isOk]
          ? h.fromSuccess($val)
          : this
      ;
  };
  
subject: fix FP immutability of and()