Go Web Service - Undefined type has no field or method [duplicate]

Question

I am trying to consolidate routing functionality within a web service. The package main has two files of concern, route.go and main.go.

Within route.go I am defining routing as follows:

package main

import (
    "github.com/justinas/alice"
    "net/http"
)

func (app *Application) Routes() http.Handler {
    standardMiddleware := alice.New(app.logRequest)

    mux := http.NewServeMux()
    mux.HandleFunc("/ping", helpers.Ping)

    return standardMiddleware.Then(mux)
}

Within main.go I am trying to execute the application as follows:

package main

import (
    "flag"
    "log"
    "net/http"
    "os"
)

type Application struct {
    errorLog *log.Logger
}

func main() {
    addr := flag.String("addr", ":8080", "HTTP Network Address")
    flag.Parse()

    errorLog := log.New(os.Stderr, "ERROR\t", log.Ldate|log.Ltime|log.Lshortfile)

    app := &Application{
        errorLog: errorLog,
    }

    srv := &http.Server{
        Addr:     *addr,
        ErrorLog: errorLog,
        Handler:  app.Routes(),
    }

    err := srv.ListenAndServe()
    errorLog.Fatal(err)
}

When I execute the program I get the following error: app.Routes undefined (type *Application has no field or method Routes)

I'm not sure why the method isn't registering correctly?