[Haskell-beginners] Re: global variables
prad at towardsfreedom.com
Sun Aug 15 14:04:11 EDT 2010
On Wed, 11 Aug 2010 22:25:45 +0200
Ertugrul Soeylemez <es at ertes.de> wrote:
> My way of doing this is the following (snippet):
> import Control.Applicative
> import MonadLib
> type DatabaseT = ReaderT Connection
> myApplication :: DatabaseT IO ()
> myApplication = do
> dbConn <- ask
> inBase $ runRaw dbConn "SELECT now();"
> runDatabaseT :: BaseM m IO => DatabaseT m a -> m a
> runDatabaseT c = do
> conn <- inBase $ connectPostgreSQL ""
> runReaderT (Config conn) c
> main :: IO ()
> main = runDatabaseT myApplication
thank you ertugrul. i understand the explanations you and MAN have
provided regarding global variables.
however, i don't understand what you have done above despite the
illustrative game example. i've been in the middle of trying to get
info out of a monad (as indicated in other posts) and have finally
gotten by the errors (although the understanding hasn't quite congealed
yet). as a result i haven't been able to try to incorporate the above
yet (which is why i haven't responded till now).
i did note that MonadLib doesn't seem to exist, so is that something i
get from cabal? is ask part of it too?
> What you want is not a global variable, but a convenient way to pass
> environment values to functions and computations.
yes that is what i want, but i haven't gotten the gist of the code you
have provided me with yet. i need to understand types better for one
> I hope this helps.
it will. i've flagged your post and will come back to it after
acquiring a bit more competence - as well as repetitive readings.
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