There are no global variables in Haskell... You can have the names in the widest namespace, but there's no modification allowed. Whether you define your connection in the main, or at top (module) level, when you pass it to a function, it'll be copied. In your example code your defining a function 'fn' which has this signature: fn :: Connection -> a -> IO b But the Connection that 'fn' gets is a parameter, not a global. Ertugrul's approach is the correct one: you define your functions letting the transformers take care of the plumbing, and the params get passed around for you. El mié, 11-08-2010 a las 12:54 -0700, prad escribió:
i'm curious about the best way to deal with conn to make db connections.
i define it in main like this, then when i want to use it in a function i have to pass it as a parameter:
main = do conn <- connectPostgreSQL ... fn conn something
fn conn x = ...
now conn is a global variable i guess because it is defined in main, but perhaps main isn't considered a global namespace? i recall in python a global variable could be accessed by functions, but in php they can't unless you use "global" within the function.
so is this the correct way to handle such things? right now it seems to be the only way in haskell.