What if a value constructor should also be a type?

I am in case that a value constructor of a data type should be also a type, e.g if I have:

data Person = Student {开发者_如何学JAVAname :: String, age :: Int}
            | Staff {name :: String, salary :: Float} deriving (Show)

I misused like this way:

type St = Student

or anywhere that use Student as type, e.g [Student] is wrong too

I know I can't do this, because Student is not a type! Then how to make the value constructor Student can be used as a type? Is it out of law?

So you want Student to be a type distinct from Person and Staff? Make them different types, then.

data Person = StudentPerson Student
            | StaffPerson Staff
              deriving (Show)

data Student = Student {name :: String, age :: Int} deriving (Show)
data Staff = Staff {name :: String, salary :: Float} deriving (Show)

They're different types now. You can control what it is you want. And you don't accidentally generate partial functions like age and salary are in your case, either.