Hallo list,
I don't quite get how ($!) works. I have this function:
dbCreateIndices con dtn dof = do
let dummy = newDbItem
let query = "SELECT id FROM " ++ (dtn dummy) ++ " ORDER BY " ++ (dof dummy)
ids <- liftM (map fromSql . concat ) $! quickQuery con query []
return $ IntMap.fromList $ zip ids [0..]
quickQuery returns a lazy list of results, and I expected ($!) to make
it strict. But my program crashes if I use it this way. But, if I add
a print to the function:
dbCreateIndices con dtn dof = do
let dummy = newDbItem
let query = "SELECT id FROM " ++ (dtn dummy) ++ " ORDER BY " ++ (dof dummy)
ids <- liftM (map fromSql . concat ) $! quickQuery con query []
print ids
return $ IntMap.fromList $ zip ids [0..]
print makes the ids list strict and all is well. How is the correct
way to use ($!) ?
Cheers,
--
-alex
http://www.ventonegro.org/
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