[Haskell-cafe] Webdriver: Couldn't match type `Element' with `WD Element'

[Cody Goodman]

I've posted this question to stackoverflow:
https://stackoverflow.com/questions/24650813/find-all-text-inputs-on-webpage-with-haskell-webdriver-package

On Tue, Jul 8, 2014 at 6:16 PM, Cody Goodman
<codygman.consulting at gmail.com> wrote:
> That gave a syntax error, however this was valid:
>
>     let textElems = filter ((==) "text" . (`attr` "type")) inputs
>
> It then gave me some ambiguous type errors:
>
>     {-# LANGUAGE OverloadedStrings #-}
>
>     import           Control.Monad
>     import           Control.Monad.IO.Class
>     import qualified Data.Text                    as T
>     import           Test.WebDriver
>     import           Test.WebDriver.Classes       (WebDriver (..))
>     import           Test.WebDriver.Commands
>     import           Test.WebDriver.Commands.Wait
>
>     main = do
>       runSession defaultSession capabilities $ do
>           openPage "http://www.appnitro.com/demo/view.php?id=1"
>           inputs <- findElems $ ByTag "input"
>           let textElems = filter ((==) ("text") . (`attr` "type"))
> inputs :: [Element]
>           -- wait 20 seconds
>           waitUntil 20 (getText <=< findElem $ ByCSS ".doesnotexist")
>             `onTimeout` return ""
>       liftIO $ putStrLn "done"
>         where
>           capabilities = allCaps { browser=firefox }
>
>
>     -- Prelude Control.Monad Control.Monad.IO.Class
> Control.Monad.Trans.Class> :r
>     -- [1 of 1] Compiling Main             ( src/Main.hs, interpreted )
>
>     -- src/Main.hs:15:31:
>     --     No instance for (Eq (wd0 (Maybe T.Text)))
>     --       arising from a use of ‘==’
>     --     The type variable ‘wd0’ is ambiguous
>     --     Note: there are several potential instances:
>     --       instance Eq a => Eq (GHC.Real.Ratio a) -- Defined in ‘GHC.Real’
>     --       instance Eq (Test.WebDriver.Common.Profile.PreparedProfile b)
>     --         -- Defined in ‘Test.WebDriver.Common.Profile’
>     --       instance Eq (Test.WebDriver.Common.Profile.Profile b)
>     --         -- Defined in ‘Test.WebDriver.Common.Profile’
>     --       ...plus 27 others
>     --     In the first argument of ‘(.)’, namely ‘(==) ("text")’
>     --     In the first argument of ‘filter’, namely
>     --       ‘((==) ("text") . (`attr` "type"))’
>     --     In the expression:
>     --         filter ((==) ("text") . (`attr` "type")) inputs :: [Element]
>
>     -- src/Main.hs:15:37:
>     --     No instance for (Data.String.IsString (wd0 (Maybe T.Text)))
>     --       arising from the literal ‘"text"’
>     --     The type variable ‘wd0’ is ambiguous
>     --     Note: there is a potential instance available:
>     --       instance a ~ Data.ByteString.Internal.ByteString =>
>     --                Data.String.IsString
>     --
> (attoparsec-0.12.1.0:Data.Attoparsec.ByteString.Internal.Parser a)
>     --         -- Defined in
> ‘attoparsec-0.12.1.0:Data.Attoparsec.ByteString.Char8’
>     --     In the first argument of ‘(==)’, namely ‘("text")’
>     --     In the first argument of ‘(.)’, namely ‘(==) ("text")’
>     --     In the first argument of ‘filter’, namely
>     --       ‘((==) ("text") . (`attr` "type"))’
>
> I then remembered that the type of attr is  WebDriver wd => Element ->
> Text -> wd (Maybe Text) and made this change:
>
>     - let textElems = filter ((==) ("text") . (`attr` "type")) inputs
> :: [Element]
>     + let textElems = filter ((==) (Just "text" :: Maybe T.Text) .
> (`attr` "type")) inputs :: [Element]
>
> and got what I believe to be a monadic error:
>
>     Prelude Control.Monad Control.Monad.IO.Class Control.Monad.Trans.Class> :r
>     [1 of 1] Compiling Main             ( src/Main.hs, interpreted )
>
>     src/Main.hs:15:69:
>         Couldn't match type ‘Maybe T.Text’ with ‘T.Text’
>         Expected type: Element -> Maybe T.Text
>           Actual type: Element -> Maybe (Maybe T.Text)
>         In the second argument of ‘(.)’, namely ‘(`attr` "type")’
>         In the first argument of ‘filter’, namely
>           ‘((==) (Just "text" :: Maybe T.Text) . (`attr` "type"))’
>         In the expression:
>             filter
>               ((==) (Just "text" :: Maybe T.Text) . (`attr` "type")) inputs ::
>               [Element]
>     Failed, modules loaded: none.
>
> This led me to make this change:
>
>     -let textElems = filter ((==) (Just "text" :: Maybe T.Text) .
> (`attr` "type")) inputs :: [Element]
>     +let textElems = filter ((==) (return $ Just "text" :: Maybe
> T.Text) . (`attr` "type")) inputs :: [Element]
>
> and I got the following error:
>
>     src/Main.hs:15:78:
>         Couldn't match type ‘Maybe T.Text’ with ‘T.Text’
>         Expected type: Element -> Maybe T.Text
>           Actual type: Element -> Maybe (Maybe T.Text)
>         In the second argument of ‘(.)’, namely ‘(`attr` "type")’
>         In the first argument of ‘filter’, namely
>           ‘((==) (return $ Just "text" :: Maybe T.Text) . (`attr` "type"))’
>         In the expression:
>             filter
>               ((==) (return $ Just "text" :: Maybe T.Text) . (`attr` "type"))
>               inputs ::
>               [Element]
>     Failed, modules loaded: none.
>
> On Tue, Jul 8, 2014 at 6:02 PM, Brandon Allbery <allbery.b at gmail.com> wrote:
>>
>> On Tue, Jul 8, 2014 at 6:52 PM, Cody Goodman <codygman.consulting at gmail.com>
>> wrote:
>>>
>>>       textElems <- filterM (liftM $ ((==) "text" . (`attr` "type")))
>>> inputs
>>
>>
>> Are you sure this shouldn't be:
>>
>>     let textElems = filter ((==) "text" . `attr` "type") inputs
>>
>> ? The type in the error suggests this is more appropriate.
>>
>> --
>> brandon s allbery kf8nh                               sine nomine associates
>> allbery.b at gmail.com                                  ballbery at sinenomine.net
>> unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net