channel Signup {
	out accounts(accountDB:Map, signUp(accountId:Str, name:Str)) = if(contains(accountDB, accountId), 
																		accountDB, 
																		insert(accountDB, accountId, {"name": name, "tweets": nil}))
}

channel Tweet(accountId:Str) {
	out accounts.{accountId}.tweets(tweetList:List, tweet(contents:Str)) = append(tweetList, contents)
}