import Database.HDBC
import Database.HDBC.PostgreSQL
import Data.List

type SQL = String

data Relation = Relation SQL
  deriving (Show)

sql (Relation sql) = sql

printTuples conn rel =
    quickQuery' conn ("SELECT DISTINCT * FROM " ++ (sql rel)) []

join rel1 rel2 =
    Relation ((sql rel1) ++ " NATURAL JOIN " ++ (sql rel2))

project fields rel1 =
    Relation ("(SELECT " ++ (intercalate "," fields) ++ " FROM " ++ (sql rel1) ++ ") a")

(π) = project
(⋈) = join