[Haskell-beginners] Re: ghci access to .hs functions

[MAN]

Hey prad, I was checking out your code and noticed a couple of things
you could be interested to know.

Your main will allways be 'IO ()' , but that doesn't mean you must
sparkle 'return ()' all over the place :P Check this out:

main = do
    args <- getArgs
    let act = head args
    conn <- connectPostgreSQL "host=localhost dbname=lohv user=pradmin"
    case act of 
         "add"  -> do
             kV1 <- dbDef conn
             upDbs conn (fromSql kV1)
         "upd"  -> upDbs conn (last args)
         "all"  -> gtKys conn
         _      -> putStrLn "add, upd num, all only!!" 
    commit conn
    disconnect conn
    putStrLn "All Done!"

I took the liberty of modifying your gtKys function:

-- gtKys: gets all key values in database [NOTICE mapM_ for mapM]
gtKys :: (IConnection conn) => conn -> IO ()
gtKys conn = do
    r <- quickQuery conn "SELECT key from main" []
    let kL = concat $ map (map fromSql) r
    mapM_ (mkPag conn) kL

Only if 'upDbs' return some value inside IO you'd replace their calls
for " upDbs conn some >> return () ". Although I assume those statements
are simple 'IO ()', just like 'putStrLn string'


El jue, 12-08-2010 a las 01:42 -0700, prad escribió:
> On Thu, 12 Aug 2010 09:01:42 +0100
> Brent Yorgey <byorgey at seas.upenn.edu> wrote:
> 
> > Can you show
> > us the exact contents of your .hs file?
> certainly! but now i take it all back! :(
> it's working fine without the return().
> 
> it compiles main when i :l or when i ghci the file from the command
> line.
> 
> so now i think i'm delusional. :D :D
> 
> anyway, here's some of the code below and i'll ask another question. in
> the function:
> 
> -- edFil: edits a file with vim
> -- edFil :: String -> IO GHC.IO.Exception.ExitCode (not in scope error) 
> edFil kV = rawSystem "vim" ["+source ~/.vim/ftplugin/html/HTML.vim",kV]
> 
> i got the type from ghci, but if i actually put it in i get error:
> Not in scope: type constructor or class `GHC.IO.Exception.ExitCode'
> 
> if i don't do the type definition that ghci gives me, everything
> compiles fine.
> 
> so i don't understand the type definition, much less what's happening
> here.
> 
> ======
> import System (getArgs)
> import System.Cmd (rawSystem)
> import Data.List(elemIndices)
> import Database.HDBC
> import Database.HDBC.PostgreSQL (connectPostgreSQL)
> 
> main = do
>     args <- getArgs
>     let act = head args
>     conn <- connectPostgreSQL "host=localhost dbname=lohv user=pradmin"
>     case act of 
>          "add"  -> do
>              kV1 <- dbDef conn
>              upDbs conn (fromSql kV1)
>              return ()
>          "upd"  -> do
>              upDbs conn (last args)
>              return ()
>          "all"  -> do
>              gtKys conn
>              return ()
>          _      -> putStrLn "add, upd num, all only!!" 
>     commit conn
>     disconnect conn
>     putStrLn "All Done!"
>     return  ()
> 
> 
> -- bkS2L: break a string into a list of strings
> --  dC char delimiter; oS original string 
> bkS2L :: (Char -> Bool) -> String -> [String]
> bkS2L dC [] = []
> bkS2L dC oS = let (h,t) = break dC oS
>                   in  h : case t of
>                                []   -> []
>                                _:t  -> bkS2L dC t
> 
> -- dbDef: adds a default entry to db
> dbDef :: (IConnection conn) => conn -> IO SqlValue
> dbDef conn = do
>     run conn "INSERT INTO main DEFAULT VALUES" []
>     ((r:z):zs) <- quickQuery conn "SELECT last_value from
> main_key_seq" [] return r
> 
> -- edFil: edits a file with vim
>     -- edFil :: String -> IO GHC.IO.Exception.ExitCode (not in scope
> error) 
> edFil kV = rawSystem "vim" ["+source ~/.vim/ftplugin/html/HTML.vim",kV]
> 
> -- gtInx: gets indices for each element of substring in string
> gtInx :: (Eq a) => [a] -> [a] -> [(a,[Int])]
> gtInx hL nL = map (\x -> (x,elemIndices x hL)) nL
> 
> -- gtKys: gets all key values in database
> gtKys :: (IConnection conn) => conn -> IO [()]
> gtKys conn = do
>     r <- quickQuery conn "SELECT key from main" []
>     let kL = concat $ map (map fromSql) r
>     mapM (mkPag conn) kL
> 
> ...
> 
> =======
> 
> there are more functions, but it is all working fine.
> 
> 
>