Hi Damien, On Mon, Dec 10, 2018 at 03:18:48PM +0100, Damien Mattei wrote:
have some code that works but want to put it in a simple function without sucess:
getBD :: Connection -> String -> Float getBD conn name = noBDfp where qry_head = "select `N° BD` from sidonie.Coordonnées where Nom = ?" :: Query bd_rows = do local_bd_rows <- query conn qry_head (Only (name::String)) return local_bd_rows
i want the variable local_bd_rows accessible in the 'where' clause
how can i do that?
You don’t seem to be using the function bd_rows anywhere in the main body of the definition. You would need to do something like getBD :: Connection -> String -> IO Float getBD = do rows <- bd_rows {- code that does something with the returned data -} Note the change to the type signature—querying the database is an IO action, and therefore takes place in the IO monad. Incidently, your use of do notation in the definition of bd_rows is unnecessary: do x <- doSomething return x is actually syntactic sugar for doSomething >>= \x -> return x which the monad laws state is equivalent to just doSomething. This is a common misapprehension among Haskell novices: the do notation is just a syntactic convenience, and it is perfectly possible to write monadic functions, including in the IO monad, without it. Hope at least some of this helps. Seph -- Seph Shewell Brockway, BSc MSc (Glas.)