How to use the nearley/builtin/cow.ne function in nearley

opts.alreadycompiled.push(path)
                if (path === 'postprocessors.ne') {
                    var f = require('nearley/builtin/postprocessors.ne')
                } else if (path === 'whitespace.ne') {
                    var f = require('nearley/builtin/whitespace.ne')
                } else if (path === 'string.ne') {
                    var f = require('nearley/builtin/string.ne')
                } else if (path === 'number.ne') {
                    var f = require('nearley/builtin/number.ne')
                } else if (path === 'cow.ne') {
                    var f = require('nearley/builtin/cow.ne')
                }

                var parserGrammar = nearley.Grammar.fromCompiled(bootstraped)
                var parser = new nearley.Parser(parserGrammar)
                parser.feed(f)
                var c = Compile(parser.results[0], {
                    file: path,
                    __proto__: opts
                })

                result.rules = result.rules.concat(c.rules)
                result.body = result.body.concat(c.body)
                // result.customTokens = result.customTokens.concat(c.customTokens);
                Object.keys(c.config).forEach(function(k) {
                    result.config[k] = c.config[k]
                })
                Object.keys(c.macros).forEach(function(k) {
                    result.macros[k] = c.macros[k]
                })
            }
        } else if (productionRule.macro) {

opts.alreadycompiled.push(path);
				if (path === "postprocessors.ne") {
					var f = require("nearley/builtin/postprocessors.ne");
				} else if (path === "whitespace.ne") {
					var f = require("nearley/builtin/whitespace.ne");
				} else if (path === "string.ne") {
					var f = require("nearley/builtin/string.ne");
				} else if (path === "number.ne") {
					var f = require("nearley/builtin/number.ne");
				} else if (path === "cow.ne") {
					var f = require("nearley/builtin/cow.ne");
				}

				var parserGrammar = nearley.Grammar.fromCompiled(bootstraped);
				var parser = new nearley.Parser(parserGrammar);
				parser.feed(f);
				var c = Compile(parser.results[0], {
					file: path,
					__proto__: opts
				});

				result.rules = result.rules.concat(c.rules);
				result.body = result.body.concat(c.body);
				// result.customTokens = result.customTokens.concat(c.customTokens);
				Object.keys(c.config).forEach(function(k) {
					result.config[k] = c.config[k];
				});
				Object.keys(c.macros).forEach(function(k) {
					result.macros[k] = c.macros[k];
				});
			}
		} else if (productionRule.macro) {