yes thanks you i had swapped the arguments of map in my code, i lack sleeping those days this solution worked : let resLst = Prelude.map fromOnly bd_rows but not this: let noBD2 = Prelude.map _ bd_rows Prelude> :load UpdateSidonie [1 of 1] Compiling Main ( UpdateSidonie.hs, interpreted ) UpdateSidonie.hs:94:29: error: • Found hole: _ :: Only Text -> b Where: ‘b’ is a rigid type variable bound by the inferred type of noBD2 :: [b] at UpdateSidonie.hs:94:9-37 • In the first argument of ‘Prelude.map’, namely ‘_’ In the expression: Prelude.map _ bd_rows In an equation for ‘noBD2’: noBD2 = Prelude.map _ bd_rows • Relevant bindings include noBD2 :: [b] (bound at UpdateSidonie.hs:94:9) noBD :: Text (bound at UpdateSidonie.hs:93:9) resLst :: [Text] (bound at UpdateSidonie.hs:91:9) bd_rows :: [Only Text] (bound at UpdateSidonie.hs:86:5) qry_head :: Query (bound at UpdateSidonie.hs:79:9) qry :: [Char] (bound at UpdateSidonie.hs:77:9) (Some bindings suppressed; use -fmax-relevant-binds=N or -fno-max-relevant-binds) Valid substitutions include undefined :: forall (a :: TYPE r). GHC.Stack.Types.HasCallStack => a (imported from ‘Prelude’ at UpdateSidonie.hs:1:1 (and originally defined in ‘GHC.Err’)) | 94 | let noBD2 = Prelude.map _ bd_rows | ^ Failed, no modules loaded. it's annoying ,since i add 'import' ,i must Prelude.* basic functions: import Database.MySQL.Simple import Database.MySQL.Simple.QueryResults import Database.MySQL.Simple.Result import Control.Monad import Data.Text i must use Prelude.map, Prelude.head is there a solution to this problem? Le 07/12/2018 09:59, Francesco Ariis a écrit :
On Fri, Dec 07, 2018 at 09:44:03AM +0100, Damien Mattei wrote:
let noBD = fromOnly (Prelude.head bd_rows)
give me a solution, but i'm still searching a solution with map has in a list there could be more than one result...
So put this in your code
let noBD = map _ bd_rows
`_` will tell the compiler "tell me which type goes there". Then you can choose the appropriate function! _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
-- Damien.Mattei@unice.fr, Damien.Mattei@oca.eu, UNS / OCA / CNRS