On 10/5/05, Sebastian Sylvan <[EMAIL PROTECTED]> wrote: > On 10/4/05, Mike Crowe <[EMAIL PROTECTED]> wrote: > > Thanks, all, especially Cale for the detail. > > > > This may be unfair to ask, but is anybody willing to give an example? > > There are great examples for writing factorials. However, that's not really > > useful. I'm looking for a real-world example of using the language. > > Specifically, the first page of About Haskell states: > > WOW! I basically wrote this without testing just thinking about my program > > in terms of transformations between types. What I'm still missing is how to > > use this idea of functional programming to tie all this together. Let's > > say, for example, I want to write a data input system for a database. > > Consider these two examples: > > > > I think I understand how to take the following example (and others in that > > library) and expand to a complete UI for the data input: > > http://cvs.sourceforge.net/viewcvs.py/wxhaskell/wxhaskell/samples/wx/Grid.hs?rev=1.6&view=auto > > > > I also looked over the examples in > > http://htoolkit.sourceforge.net/ for writing to a SQL > > database. So I can see how to save the data. The following example I get > > for inserting: > > insertRecords :: Connection -> IO () > > insertRecords c = do > > execute c "insert into Test(id,name) values (1,'Test1')" > > > > How, though, would I start? If I did this in an imperative language, I > > might do it like (in Python): > > > > def main: > > if gridCtrl.Show(): # returns True if user exits > > pressing Save > > data = gridCtrl.getData() > > dataBase.insertRecords(data) > > > > In Haskell, how would you start this at the top? How would you define a > > relationship between two modules? > > > > If this is more detailed than I should ask in this list, please LMK. > > > > Thanks! > > Mike > > In general you write a small "shell" of IO code as your base > application. This IO code then calls the rest of the > (non-IO-)functions and presents the result in some way. > > As you can see in the source code you linked you can attatch IO > actions to events. E.g. > set g [on gridEvent := onGrid] > > So to, for example, trigger a database update when the user presses a > button, you would attatch the database-update action to the on click > event for that button. > > You could also use partial application to pass along extra data that > this function may need > > set but [on click := updateDB dbConnection] > > where dbConnection is some value representing a database connection > > and then in the function defintion: > > updateDB dbConn = do ... > > As you can see onGrid takes two parameters (everything it needs to do > what you want it to do) but when you attatch it to the gridEvent you > only pass it the first one (the event itself passes the second one).
I meant updateDB and click-event and there respectively. Sorry. /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862 _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
