displaying database content in wxHaskell - haskell

Question

Im using tutorials from wxHaskell and want to display content of table movies in the grid.
HEre is my code :
{--------------------------------------------------------------------------------
Test Grid.
--------------------------------------------------------------------------------}
module Main where
import Graphics.UI.WX
import Graphics.UI.WXCore hiding (Event)
import Database.HDBC.Sqlite3 (connectSqlite3)
import Database.HDBC
main
= start gui
gui :: IO ()
gui
= do f <- frame [text := "Grid test", visible := False]
-- grids
g <- gridCtrl f []
gridSetGridLineColour g (colorSystem Color3DFace)
gridSetCellHighlightColour g black
appendColumns g (movies) -- Here is error:
-- Couldn't match expected type `[String]'
-- against inferred type `IO [[String]]'
--appendRows g (map show [1..length (tail movies)])
--mapM_ (setRow g) (zip [0..] (tail movies))
gridAutoSize g
-- layout
set f [layout := column 5 [fill (dynamic (widget g))]
]
focusOn g
set f [visible := True] -- reduce flicker at startup.
return ()
where
movies = do
conn <- connectSqlite3 "Spop.db"
r <- quickQuery' conn "SELECT id, title, year, description from Movie where id = 1" []
let myResult = map convRow r
return myResult
setRow g (row,values)
= mapM_ (\(col,value) -> gridSetCellValue g row col value) (zip [0..] values)
{--------------------------------------------------------------------------------
Library?f
--------------------------------------------------------------------------------}
gridCtrl :: Window a -> [Prop (Grid ())] -> IO (Grid ())
gridCtrl parent props
= feed2 props 0 $
initialWindow $ \id rect -> \props flags ->
do g <- gridCreate parent id rect flags
gridCreateGrid g 0 0 0
set g props
return g
appendColumns :: Grid a -> [String] -> IO ()
appendColumns g []
= return ()
appendColumns g labels
= do n <- gridGetNumberCols g
gridAppendCols g (length labels) True
mapM_ (\(i,label) -> gridSetColLabelValue g i label) (zip [n..] labels)
appendRows :: Grid a -> [String] -> IO ()
appendRows g []
= return ()
appendRows g labels
= do n <- gridGetNumberRows g
gridAppendRows g (length labels) True
mapM_ (\(i,label) -> gridSetRowLabelValue g i label) (zip [n..] labels)
convRow :: [SqlValue] -> [String]
convRow [sqlId, sqlTitle, sqlYear, sqlDescription] = [intid, title, year, description]
where intid = (fromSql sqlId)::String
title = (fromSql sqlTitle)::String
year = (fromSql sqlYear)::String
description = (fromSql sqlDescription)::String
What should I do to get rif of error in code above (24th line)

Answer 1

The error message says that appendColumns g expects a value of type [String], but that movies is of type IO [[String]].
So you need to fix two things:
movies is an IO-action that returns a value, but you need the value it returns.
Replace
appendColumns g (movies)
with
movieList <- movies
appendColumns g movieList
(Incidentally, the brackets in the first line? They don't do anything.)
You need to feed appendColumns g a list of strings, but you are trying to give it a list of lists of strings. You either need to turn the list of lists into a list of strings, or you need to give each list of strings to appendColumns g in turn.
I'm guessing you want the latter, so you get a row on-screen for each row in the database. (I'm not familiar with wxhaskell, so I may misunderstand what appendColumns does.)
movieList <- movies
mapM_ (appendColumns g) movieList