HaskellDB - '數據庫' 變量不在範圍內

Question

我試圖運行此haskelldb Hello World示例，

module Caturday.Model.Connect where 

import Database.HaskellDB.HDBC 
import Database.HaskellDB.Sql.PostgreSQL 
import Database.HDBC.PostgreSQL (connectPostgreSQL) 

withDB :: [(String,String)] -> (Database -> IO a) -> IO a 
withDB opts = hdbcConnect generator (connectPostgreSQL conninfo) 
    where conninfo = unwords [ k ++ "=" ++ v | (k,v) <- opts ] 

opts = [("host","localhost") 
     ,("user","your_username") 
     ,("password","your_password") 
     ,("dbname","your_db_name")] 

此代碼是從site

採取做runhaskell db.hs，它拋出錯誤的，

db.hs:7:33: Not in scope: type constructor or class ‘Database’ 

而行，

withDB :: [(String,String)] -> (Database -> IO a) -> IO a 

Answer 1

Database那裏定義，它應該幫助

（https://github.com/m4dc4p/haskelldb/blob/master/src/Database/HaskellDB.hs#L68）