我有一个包含如下所示元组的数组：[((Int, Int), Int)]。我正在尝试使用列表推导创建一个新数组，如果第3个Int ==某个数字，则表示只添加所有3个Ints。我把它写成
newArray = [((x,y),z) | ((x,y),z)<-oldArray, (snd oldArray) == 5]
但是，当我尝试运行包含此代码的代码时，它表示“无法匹配预期类型”并将错误指向我的条件。 "Couldn't match expected type '(a0, Int)' with actual type '[((Int, Int), Int)]'"。
答案 0 :(得分：3)
orientdb> connect remote:localhost root root
Disconnecting from the database [null]...OK
Connecting to remote Server instance [remote:localhost] with user 'root'...OK
orientdb {server=remote:localhost/}> list databases
Found 5 databases:
* VehicleHistoryGraph (plocal)
* GratefulDeadConcerts (plocal)
* OpenBeer (plocal)
* BetterDemo (plocal)
* Tolkien-Arda (plocal)
orientdb {server=remote:localhost/}> connect plocal:../databases/GratefulDeadConcerts root root
Disconnecting from remote server [remote:localhost/]...
OK
Connecting to database [plocal:../databases/GratefulDeadConcerts] with user 'root'...
Error: com.orientechnologies.orient.core.exception.OStorageException: Cannot open local storage '../databases/GratefulDeadConcerts' with mode=rw
DB name="GratefulDeadConcerts"
Error: com.orientechnologies.orient.core.exception.OStorageException: Cannot open the storage 'GratefulDeadConcerts' because it does not exist in path: ../databases/GratefulDeadConcerts
DB name="GratefulDeadConcerts"
是一个列表，总是永远，甚至在理解范围内，因此oldArray无法应用于它。请改用snd。