Re: [Haskelldb-users] What about introducing a Connection type declaration?

[Marc W. <mar...@gm...>]

I had/have some problems with types of haskelldb so I  tried to add
type annotations.

I've used Select query mainly yet. Thus my code looks like this:

con = mysqlConnect <params>

doSomethinng con = con $ \db -> query db $  table <table>

Then I wanted to add type annotations. Thus I took the type of
	mysqlConnect :: MonadIO m => MySQLOptions -> (Database -> m a) -> m a
and removed the connection settings yielding
	mysqlConnect :: MonadIO m => (Database -> m a) -> m a
which is very much to type/reead IMHO. That's why I proposed
introducnig:
newtype CConnection :: MonadIO m => (Database -> m a) -> m a

I'm struggling here now:

line 39  is equal to 56
line 39 works fine
line 56 doesn't. Why?
Isn't  both a IO monad (because of the print statements)
After commenting out 56 it compiles.


module Modules.ObjectTree where
import Debug.Trace
import Data.FunctorM
import DBUtils
import qualified DB.VT.Ezcontentobject_tree as EOT
import qualified DB.VT.Ezcontentobject as CO
import Database.HaskellDB.HDBRec
import Database.HaskellDB
import Database.HaskellDB.Query as Q
import Data.Tree
import Monad
import Control.Monad.Trans
import Maybe
import qualified List
 
instance FunctorM Tree where
  fmapM f (Node a forest) = do
    a' <- f a
    forest' <- mapM (fmapM f) forest
    return $ Node a' forest'
 
 
type ObjectTree a = Tree  (Record a)
 
truncTree 1 (Node a _) = Node a []
truncTree x (Node a forest) = Node a $ map (truncTree (x-1)) forest
 
oT con = do
  print "blah" -- because of this we  should  have a simple IO Monad ?
  lookupField con (CO.name) (CO.ezcontentobject)  (CO.xid) (constant (1 :: Int)) >>= print :: IO () -- <<<<<<<<<<<<<<<<<<<<<<<<< 39
  return "blah"
 
-- printObjectsAsTree :: MonadIO m => ((Database -> m a) -> m a) -> Int -> IO ()
printObjectsAsTree con startid= do --<<<<<<<<<<<<<<<< 4
  print "test"
  root <- liftM head  $ lRS (EOT.parent_node_id) (constant (startid :: Int))
  print root
  --showRS root >>= putStrLn
  node <- po root
  node_show <- fmapM showRS node
  return  $ drawTree node_show
  -- return "end"
  where lRS = lookupFieldRS con (EOT.ezcontentobject_tree)
	po root = let root_id = (root!(EOT.node_id) :: Int)
		  in do  print "dumm" -- IO Monad too ?
			 print (root!(EOT.node_id))
			 lookupField con (CO.name) (CO.ezcontentobject)  (CO.xid) (constant (1 :: Int)) >>= print --  <<<<<<<<<<<<<<    56
			 return $ Node root []
			 --childs <- lRS (EOT.parent_node_id) (constant root_id)
			 --mapM_ (\r -> r!(EOT.node_id)) childs >>= print
        showRS r = do -- name <- lookupField con (CO.name) (CO.ezcontentobject) (CO.xid) (constant 1) >>= print
		      return "ab" :: IO String
		      --return $ (show $ r!node_id) ++ " (" ++ (fromJust name) ++ " )"
 
-----------------------------------------------
|| Preprocessing executables for dbez-0.0...
|| Building dbez-0.0...
|| Chasing modules from: db_ez.hs
|| [1 of 6] Skipping  DBUtils          ( DBUtils.hs, dist/build/db_ez/db_ez-tmp/DBUtils.o )
|| [2 of 6] Skipping  DB.VT.Ezcontentobject_tree ( DB/VT/Ezcontentobject_tree.hs, dist/build/db_ez/db_ez-tmp/DB/VT/Ezcontentobject_tree.o )
|| [3 of 6] Skipping  DB.VT.Ezcontentobject ( DB/VT/Ezcontentobject.hs, dist/build/db_ez/db_ez-tmp/DB/VT/Ezcontentobject.o )
|| [4 of 6] Compiling Modules.ObjectTree ( Modules/ObjectTree.hs, dist/build/db_ez/db_ez-tmp/Modules/ObjectTree.o )
|| 
Modules/ObjectTree.hs|43| 0:
||     Couldn't match `DB.VT.Ezcontentobject_tree.Contentobject_id'
|| 	   against `DB.VT.Ezcontentobject.Contentclass_id'
||       Expected type: RecCons DB.VT.Ezcontentobject_tree.Contentobject_id
|| 			     (Maybe Int)
|| 			     vr
||       Inferred type: RecCons DB.VT.Ezcontentobject.Contentclass_id
|| 			     Int
|| 			     vr1
||     When using functional dependencies to combine
||       Database.HaskellDB.Database.GetRec (RecCons f (Expr a) er)
|| 					 (RecCons f a vr),
|| 	arising from the instance declaration at Imported from Database.HaskellDB.Database
||       Database.HaskellDB.Database.GetRec (RecCons DB.VT.Ezcontentobject_tree.Contentobject_id
|| 						  (Expr (Maybe Int))
													[...]
|| 																						(RecCons DB.VT.Ezcontentobject_tree.Sort_order
|| 																							 (Expr (Maybe Int))
|| 																							 RecNil))))))))))))))))
|| 					 (RecCons DB.VT.Ezcontentobject.Contentclass_id Int vr),
arising from use of `lookupFieldRS' at Modules/ObjectTree.hs|52| 14-26
||     When generalising the type(s) for `printObjectsAsTree'
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