[Haskell-cafe] IO Monad/ haskelldb strange error?

8 Aug 2006

      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 fine

Any suggestion appreciated.. I'm struggling for some hours now..

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
  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'

[Haskell-cafe] IO Monad/ haskelldb strange error?

Marc Weber