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... D Le 06/12/2018 17:10, Francesco Ariis a écrit :
On Thu, Dec 06, 2018 at 03:54:45PM +0100, Damien Mattei wrote:
if it was so easy!
Damien, you must heed the compiler!
heed?
UpdateSidonie.hs:93:25: error: • Couldn't match expected type ‘Only a’ with actual type ‘[Only Text]’ • In the first argument of ‘fromOnly’, namely ‘bd_rows’ In the expression: fromOnly bd_rows In an equation for ‘noBD’: noBD = fromOnly bd_rows • Relevant bindings include noBD :: a (bound at UpdateSidonie.hs:93:9) | 93 | let noBD = fromOnly bd_rows | ^^^^^^^ Failed, no modules loaded.
So you applied `fromOnly` to `bd_rows`. fromOnly has type
fromOnly :: Only a -> a
Now GHC is complaining:
• I was expecting ‘Only a’ but you gave me ‘[Only Text]’
So either call "head" on [Only Text] (unsafe!) or map over it. See if it works and if not, fire again here -F _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners