main.go

"createSong": &graphql.Field{
	Type: songType,
	Args: graphql.FieldConfigArgument{
		"id": &graphql.ArgumentConfig{
			Type: graphql.NewNonNull(graphql.String),
		},
		"album": &graphql.ArgumentConfig{
			Type: graphql.NewNonNull(graphql.String),
		},
		"title": &graphql.ArgumentConfig{
			Type: graphql.NewNonNull(graphql.String),
		},
		"duration": &graphql.ArgumentConfig{
			Type: graphql.NewNonNull(graphql.String),
		},
	},
	Resolve: func(params graphql.ResolveParams) (interface{}, error) {
		var song Song
		song.ID = params.Args["id"].(string)
		song.Album = params.Args["album"].(string)
		song.Title = params.Args["title"].(string)
		song.Duration = params.Args["duration"].(string)
		songs = append(songs, song)
		return song, nil
	},
},