Understanding Haskell postgresql connection function type error

I am java programmer reading and learning haskell now. I am trying write a simple program to connect (and disconnect) to postgres database using HDBC postgres driver. For simplicity i don't have any other logic in it.

It is throwing a function type error. I indented the code correct and if I remove disconnect then it works with the defined type.

Can some one shed some light on what i am missing defining the type for this function? i would apriciate your help.

thanks!

sample code:

import Database.HDBC
import Database.HDBC.PostgreSQL
import Database.HaskellDB
import Database.HaskellDB.HDBC.PostgreSQL

tryConnect :: Int  -> (Database -> IO Connection) -> ()   
tryConnect id =
   do
     c <- postgresqlConnect [("host","dbhost"),("dbname","db1"),("user","开发者_Python百科user1"),("password","test")]
     disconnect c
     return ()

I am getting the following error from GHCi

   Couldn't match expected type `(Database -> IO Connection) -> a'
       against inferred type `IO ()'
In a stmt of a 'do' expression: disconnect c
In the expression:
    do { c <- postgresqlConnect
                [("host", "dbhost"), ("dbname", "db1"), ....];
         disconnect c;
         return () }
In the definition of `insrt':
    insrt id
            = do { c <- postgresqlConnect [("host", "dbhost"), ....];
                   disconnect c;
                   return () }

Failed, modules loaded: none.

The problem is that you haven't provided enough arguments to postgresqlConnect. Its type signature is [(String, String)] -> (Database -> m a) -> m a, but you've only provided the first argument. Giving postgresqlConnect its second argument should solve the problem, and you'll be able to change the type declaration back to Int -> IO ().

EDIT: The answer below is totally wrong. My bad.

Well, the type signature is tryConnect :: Int -> (Database -> IO Connection) -> (). Generally this would indicate that the function takes an Int and a (Database -> IO Connection) and returns (), but the only parameter you've supplied in the function definition is id. Therefore, you actually have a function that takes an Int and returns a new function with the type signature (Database -> IO Connection) -> ().

So, to conclude, it seems there's a parameter in the type signature that you haven't used in the actual function. Either remove that function from the type signature, or change the function to be tryConnect id func = ... rather than tryConnect id = ....